arXiv daily: Solar and Stellar Astrophysics (astro-ph.SR)

Authors:Santana Mansfield, Pavel Kroupa

Abstract: Low-mass models of M-dwarfs that undergo the convective kissing instability fluctuate in luminosity and temperature resulting in a gap in the main sequence that is observed in the $Gaia$ data. During this instability, the models have repeated periods of full convection where the material is mixed throughout the model. Stellar evolution models are performed using MESA with varying amounts of convective overshooting and semi-convection. We find that the amplitude and intensity of the instability is reduced with increasing amounts of overshooting but sustained when semi-convection is present. This is reflected in the loops in the evolutionary tracks in the Hertzsprung-Russell diagram. The surface abundances of $^1$H, $^3$He, $^4$He, $^{12}$C, $^{14}$N and $^{16}$O increase or decrease over time due to the convective boundary, however the relative abundance changes are very small and not likely observable. The mass and magnitude values from the models are assigned to a synthetic population of stars from the mass-magnitude relation to create colour-magnitude diagrams, which reproduce the M-dwarf gap as a large indent into the blueward edge of the main sequence (MS). This is featured in the luminosity function as a small peak and dip. The width of the MS decreases over time along with the difference in width between the MS at masses higher and lower than the instability. The parallel offset and relative angle between the upper and lower parts of the MS also change with time along with the mass-magnitude relation. Potential age-dating methods for single stars and stellar populations are described.

Authors:R. D. Jeffries Keele University, UK, R. J. Jackson Keele University, UK, A. S. Binks MIT Kavli Institute for Astrophysics and Space Research, USA

Abstract: IC 4665 is one of only a dozen young open clusters with a ``lithium depletion boundary" (LDB) age. Using an astrometrically and spectroscopically filtered sample of cluster members, we show that both the positions of its low mass stars in Gaia absolute colour-magnitude diagrams and the lithium depletion seen among its K- and early M-stars are discordant with the reported LDB age of (32 +4/-5) Myr. Re-analysis of archival spectra suggests that the LDB of IC 4665 has not been detected and that the published LDB age should be interpreted as a lower limit. Empirical comparisons with similar datasets from other young clusters with better-established LDB ages indicate that IC 4665 is bracketed in age by the clusters IC 2602 and IC 2391 at (55 +/- 3) Myr.

Authors:V. Bujarrabal, J. Alcolea, A. Castro-Carrizo, J. Kluska, C. Sanchez Contreras, H. Van Winckel

Abstract: We aim to study the dust distribution in the central regions of the Keplerian disk of the Red Rectangle, the prototype of binary post-AGB stars with rotating circumbinary disks, and to compare it with the distribution of relevant molecular gas tracers We present new high-resolution (20 milliarcseconds, mas) ALMA observations of continuum and line emissions at 0.9 mm. The maps have been analyzed by means of a simple model of dust and free-free emissionn that is able to reproduce the continuum data. Resuts: i) We find that most of the dust emission in the Red Rectangle is concentrated in the inner disk regions, with a typical size of 250 AU in diameter and 50 AU in width. ii) The settlement of dust grains onto inner equatorial regions is remarkable when compared with the relatively widespread gas distribution. iii) This region is basically coincident with the warm PDR (photo-dominated region) where CI, CII, and certain molecules such as HCN are presumably formed, as well as probably PAHs (polycyclic aromatic hydrocarbons, whose emission is very strong in this source). iv) We confirm the large size of the grains, with a typical radius ~ 150 mu The opacity of dust at 0.9 mm is deduced to be relatively large, ~0.5. v) We also confirm the existence of a very compact HII region in the center, for which we measure an extent of 10 - 15 mas (~ 10 AU) and a total flux of 7 - 8 mJy at 0.9 mm.

Authors:Gabriella Zsidi, C. J. Nixon, T. Naylor, J. E. Pringle, K. L. Page

Abstract: We present the discovery of an unusual set of flares in the nova-like variable V704 And. Using data from AAVSO, ASAS-SN, and ZTF, of the nova-like variable V704 And, we have discovered a trio of brightening events that occurred during the high state. These events elevate the optical brightness of the source from $\sim13.5$ magnitude to $\sim12.5$ magnitude. The events last for roughly a month, and exhibit the unusual shape of a slow rise and faster decay. Just after the third event we obtained data from regular monitoring with Swift, although by this time the flares had ceased and the source returned to its pre-flare level of activity in the high-state. The Swift observations confirm that during the high-state the source is detectable in the X-rays, and provide simultaneous UV and optical fluxes. As the source is already in the high-state prior to the flares, and thus the disc is expected to already be in the high-viscosity state, we conclude that the driver of the variations must be changes in the mass transfer rate from the companion star and we discuss possible mechanisms for such short-timescale mass transfer variations to occur.

Authors:Daniela P. Iglesias, Olja Panić, Isabel Rebollido

Abstract: eta Telescopii is a ~23 Myr old A-type star surrounded by an edge-on debris disc hypothesised to harbour gas. Recent analysis of far- and near-ultraviolet spectroscopic observations of eta Tel found absorption features at ~-23 km/s and ~-18 km/s in several atomic lines, attributed to circumstellar and interstellar gas, respectively. In this work, we put the circumstellar origin of the gas to a test by analysing high resolution optical spectroscopy of eta Tel and of three other stars with a similar line of sight as eta Tel: HD 181327, HD 180575, and rho Tel. We found absorption features at ~-23 km/s and ~-18 km/s in the Ca ii H&K lines, and at ~-23 km/s in the Na i D1&D2 doublet in eta Tel, in agreement with previous findings in the ultraviolet. However, we also found absorption features at ~-23 km/s in the Ca ii K lines of the three other stars analysed. This strongly implies that the absorption lines previously attributed to circumstellar gas are more likely due to an interstellar cloud traversing the line of sight of eta Tel instead.

Authors:Peter W. Schuck, Mark G. Linton

Abstract: Magnetic helicity, $H$, measures magnetic linkages in a volume. The early theoretical development of helicity focused on magnetically closed systems in $\mathcal{V}$ bounded by $\mathcal{S}$. For magnetically closed systems, $\mathcal{V}\in\mathbb{R}^3=\mathcal{V}+\mathcal{V}^*$, no magnetic flux threads the boundary, $\hat{\boldsymbol{n}}\cdot\boldsymbol{B}|_\mathcal{S}=0$. Berger and Field (1984) and Finn and Antonsen (1985) extended the definition of helicity to relative helicity, $\mathcal{H}$, for magnetically open systems where magnetic flux may thread the boundary. Berger (1999,2003) expressed this relative helicity as two gauge invariant terms that describe the self helicity of magnetic field that closes inside $\mathcal{V}$ and the mutual helicity between the magnetic field that threads the boundary $\mathcal{S}$ and the magnetic field that closes inside $\mathcal{V}$. The total magnetic field that permeates $\mathcal{V}$ entangles magnetic fields that are produced by current sources $\boldsymbol{J}$ in $\mathcal{V}$ with magnetic fields that are produced by current sources $\boldsymbol{J}^*$ in $\mathcal{V}^*$. Building on this fact, we extend Berger's expressions for relative magnetic helicity to eight gauge invariant quantities that simultaneously characterize both of these self and mutual helicities and attribute their origins to currents $\boldsymbol{J}$ in $\mathcal{V}$ and/or $\boldsymbol{J}^*$ in $\mathcal{V}^*$, thereby disentangling the domain of origin for these entangled linkages. We arrange these eight terms into novel expressions for internal and external helicity (self) and internal-external helicity (mutual) based on their domain of origin. The implications of these linkages for interpreting magnetic energy is discussed and new boundary observables are proposed for tracking the evolution of the field that threads the boundary.

Authors:Sargam M. Mulay, Lyndsay Fletcher, Hugh Hudson, Nicolas Labrosse

Abstract: We have systematically investigated ultraviolet (UV) emission from molecular hydrogen (H$_{2}$) using the Interface Region Imaging Spectrometer (IRIS), during three X-ray flares of C5.1, C9.7 and X1.0 classes on Oct. 25, 2014. Significant emission from five H$_{2}$ spectral lines appeared in the flare ribbons, interpreted as photo-excitation (fluorescence) due to the absorption of UV radiation from two Si IV spectral lines. The H$_{2}$ profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red (blue) wing components showed small redshifts (blue shifts) of ~5-15 km s$^{-1}$ (~5-10 km s$^{-1}$). The nonthermal velocities were found to be ~5-15 km s$^{-1}$. The interrelation between intensities of H$_{2}$ lines and their branching ratios confirmed that H$_{2}$ emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si IV and H$_{2}$ emission, but the H$_{2}$ emission is more extended and diffuse, further suggesting H$_{2}$ fluorescence, and - by analogy with flare ''back-warming'' providing a means to estimate the depth from which the H$_{2}$ emission originates. We find that this is 1871$\pm$157 km and 1207$\pm$112 km below the source of the Si IV emission, in two different ribbon locations.

Authors:Kishalay De, Fiona A. Daly, Roberto Soria

Abstract: High mass X-ray binaries hosting red supergiant (RSG) donors are a rare but crucial phase in massive stellar evolution, with only one source previously known in the Milky Way. In this letter, we present the identification of the second Galactic RSG X-ray binary SWIFT J0850.8-4219. We identify the source 2MASS 08504008-4211514 as the likely infrared counterpart with a chance coincidence probability $\approx 5 \times 10^{-6}$. We present a $1.0 - 2.5\,\mu$m spectrum of the counterpart, exhibiting features characteristic of late-type stars and an exceptionally strong He I emission line, corroborating the identification. Based on i) the strength of the $^{12}$CO(2,0) band, ii) strong CN bandheads and absent TiO bandheads at $\approx 1.1\,\mu$m and iii) equivalent width of the Mg I $1.71\,\mu$m line, we classify the counterpart to be a K3$-$K5 type RSG with an effective temperature of $3820 \pm 100$ K, located at a distance of $\approx 12$ kpc. We estimate the source X-ray luminosity to be $(4 \pm 1) \times 10^{35}$ erg s$^{-1}$, with a hard photon index ($\Gamma < 1$), arguing against a white dwarf accretor but consistent with a magnetized neutron star in the propeller phase. Our results highlight the potential of systematic NIR spectroscopy of Galactic hard X-ray sources in completing our census of the local X-ray binary population.

Authors:You Wu, Jiao Li, Chao Liu, Yi Hu, Long Xu, Tanda Li, Xuefei Chen, Zhanwen Han

Abstract: Wide binaries play a crucial role in analyzing the birth environment of stars and the dynamical evolution of clusters. When wide binaries are located at greater distances, their companions may overlap in the observed images, becoming indistinguishable and resulting in unresolved wide binaries, which are difficult to detect using traditional methods. Utilizing deep learning, we present a method to identify unresolved wide binaries by analyzing the point-spread function (PSF) morphology of telescopes. Our trained model demonstrates exceptional performance in differentiating between single stars and unresolved binaries with separations ranging from 0.1 to 2 physical pixels, where the PSF FWHM is ~2 pixels, achieving an accuracy of 97.2% for simulated data from the Chinese Space Station Telescope. We subsequently tested our method on photometric data of NGC 6121 observed by the Hubble Space Telescope. The trained model attained an accuracy of 96.5% and identified 18 wide binary candidates with separations between 7 and 140 au. The majority of these wide binary candidates are situated outside the core radius of NGC 6121, suggesting that they are likely first-generation stars, which is in general agreement with the results of Monte Carlo simulations. Our PSF-based method shows great promise in detecting unresolved wide binaries and is well suited for observations from space-based telescopes with stable PSF. In the future, we aim to apply our PSF-based method to next-generation surveys such as the China Space Station Optical Survey, where a larger-field-of-view telescope will be capable of identifying a greater number of such wide binaries.

Authors:Arnab Sarkar, Lev Yungelson, Christopher A. Tout

Abstract: We extend a magnetic braking (MB) model, which has been used earlier to address the evolution of cataclysmic variables, to address the spin period $P_\mathrm{spin}$ evolution of fully convective M dwarf (FCMD) stars. The MB mechanism is an $\alpha-\Omega$ dynamo, which leads to stellar winds that carry away angular momentum. We model our MB torque such that the FCMDs experience a MB torque, approximately scaling as $P_\mathrm{spin}^{-1}$ at shorter periods, before transitioning into a Skumanich-type MB torque, scaling as $P_\mathrm{spin}^{-3}$. We also implement a parametrized reduction in the wind mass loss owing to the entrapment of winds in dead zones. We choose a set of initial conditions and vary the two free parameters in our model to find a good match of our spin trajectories with open clusters containing FCMDs such as NGC2547, Pleiades, NGC2516 and Praesepe. We find that our model can explain the long spin periods of field stars and that a spread in spin distribution persists till over 3 Gyr. An advantage of our model is in relating physically motivated estimations of the magnetic field strength and stellar wind to properties of the stellar dynamo, which other models often remain agnostic about. We track the spin dependence of the wind mass losses, Alfv\'en radii and surface magnetic fields and find good agreement with observations. We discuss the implications of our results on the effect of the host FCMD on any orbiting exoplanets and our plans to extend this model to explain solar-like stars in the future.

Authors:Gábor B. Kovács, János Nuspl, Róbert Szabó

Abstract: Nonlinear pulsation modeling of classical variable stars is among the first topics which were developed at the beginning of the computational era. Various developments were made, and many questions were answered in the past 60 years, and the models became more complex, describing the genuinely 3D convection in a single dimension. Despite its successes, the recent public availability of the MESA Radial Stellar Pulsations (MESA RSP) module and the emerging results from multidimensional codes made clear that the 8 free convective parameters, unique to these models, together with the underlying physical models need calibration. This could be done by comparing them against multi-dimensional codes, but before that, it is important to scrutinize the free parameters of the 1D codes using observations. This is a follow-up work of our previous calibration on the convective parameters of the Budapest-Florida and MESA RSP pulsation codes for RRab stars. In this paper, we extend the previous calibration to the RRc stars and the RR Lyrae stars in general. We found that correlations of some of the parameters are present in RRc stars as well but have a different nature, while high-temperature RRc stars' pulsation properties are very sensitive to the chosen parameter sets.

Authors:E. Aydi, L. Chomiuk, J. Strader, K. V. Sokolovsky, R. E. Williams, D. A. H. Buckley, A. Ederoclite, L. Izzo, R. Kyer, J. D. Linford, A. Kniazev, B. D. Metzger, J. Mikolajewska, P. Molaro, I. Mollina, K. Mukai, U. Munari, M. Orio, T. Panurach, B. J. Shappee, K. J. Shen, J. L. Sokoloski, R. Urquhart, F. M. Walter

Abstract: The optical spectra of novae are characterized by emission lines from the hydrogen Balmer series and either Fe II or He/N, leading to their traditional classification into two spectral classes: "Fe II" and "He/N". For decades, the origins of these spectral features were discussed in the literature in the contexts of different bodies of gas or changes in the opacity of the ejecta, particularly associated with studies by R. E. Williams and S. N. Shore. Here, we revisit these major studies with dedicated, modern data sets, covering the evolution of several novae from early rise to peak all the way to the nebular phase. Our data confirm previous suggestions in the literature that the "Fe II" and "He/N" spectral classes are phases in the spectroscopic evolution of novae driven primarily by changes in the opacity, ionization, and density of the ejecta, and most if not all novae go through at least three spectroscopic phases as their eruptions evolve: an early He/N (phase 1; observed during the early rise to visible peak and characterized by P Cygni lines of He I, N II, and N III), then an Fe II (phase 2; observed near visible peak and characterized by P Cygni lines of Fe II and O I), and then a later He/N (phase 3; observed during the decline and characterized by emission lines of He I. He II, N II, and N III), before entering the nebular phase. This spectral evolution seems to be ubiquitous across novae, regardless of their speed class; however the duration of each of these phase differs based on the speed class of the nova.

Authors:S. Tinyanont, R. J. Foley, K. Taggart, K. W. Davis, N. LeBaron, J. E. Andrews, M. J. Bustamante-Rosell, Y. Camacho-Neves, R. Chornock, D. A. Coulter, L. Galbany, S. W. Jha, C. D. Kilpatrick, L. A. Kwok, C. Larison, J. R. Pierel, M. R. Siebert, G. Aldering, K. Auchettl, J. S. Bloom, S. Dhawan, A. V. Filippenko, K. D. French, A. Gagliano, M. Grayling, W. V. Jacobson-Galán, D. O. Jones, X. Le Saux, P. Macias, K. S. Mandel, C. McCully, E. Padilla Gonzalez, A. Rest, C. Rojas-Bravo, M. F. Skrutskie, S. Thorp, Q. Wang, S. M. Ward

Abstract: We present the Keck Infrared Transient Survey (KITS), a NASA Key Strategic Mission Support program to obtain near-infrared (NIR) spectra of astrophysical transients of all types, and its first data release, consisting of 105 NIR spectra of 50 transients. Such a data set is essential as we enter a new era of IR astronomy with the James Webb Space Telescope (JWST) and the upcoming Nancy Grace Roman Space Telescope (Roman). NIR spectral templates will be essential to search JWST images for stellar explosions of the first stars and to plan an effective Roma} SN Ia cosmology survey, both key science objectives for mission success. Between 2022 February and 2023 July, we systematically obtained 274 NIR spectra of 146 astronomical transients, representing a significant increase in the number of available NIR spectra in the literature. The first data release includes data from the 2022A semester. We systematically observed three samples: a flux-limited sample that includes all transients $<$17 mag in a red optical band (usually ZTF r or ATLAS o bands); a volume-limited sample including all transients within redshift $z < 0.01$ ($D \approx 50$ Mpc); and an SN Ia sample targeting objects at phases and light-curve parameters that had scant existing NIR data in the literature. The flux-limited sample is 39% complete (60% excluding SNe Ia), while the volume-limited sample is 54% complete and is 79% complete to $z = 0.005$. All completeness numbers will rise with the inclusion of data from other telescopes in future data releases. Transient classes observed include common Type Ia and core-collapse supernovae, tidal disruption events (TDEs), luminous red novae, and the newly categorized hydrogen-free/helium-poor interacting Type Icn supernovae. We describe our observing procedures and data reduction using Pypeit, which requires minimal human interaction to ensure reproducibility.

Authors:Ya-Lin Wu, Yu-Chi Cheng, Li-Ching Huang, Brendan Bowler, Laird Close, Wei-Ling Tseng, Ning Chen, Da-Wei Chen

Abstract: Monitoring mass accretion onto substellar objects provides insights into the geometry of the accretion flows. We use the Lulin One-meter Telescope to monitor H$\alpha$ emission from FU Tau B, a $\sim$19 $M_{\rm Jup}$ brown-dwarf companion at 5.7" (719 au) from the host star, for six consecutive nights. This is the longest continuous H$\alpha$ monitoring for a substellar companion near the deuterium-burning limit. We aim to investigate if accretion near the planetary regime could be rotationally modulated as suggested by magnetospheric accretion models. We find tentative evidence that H$\alpha$ mildly varies on hourly and daily timescales, though our sensitivity is not sufficient to definitively establish any rotational modulation. No burst-like events are detected, implying that accretion onto FU Tau B is overall stable during the time baseline and sampling windows over which it was observed. The primary star FU Tau A also exhibits H$\alpha$ variations over timescales from minutes to days. This program highlights the potential of monitoring accretion onto substellar objects with small telescopes.

Authors:J. Borowicz, P. Pietrukowicz, P. Mróz, I. Soszyński, A. Udalski, M. K. Szymański, K. Ulaczyk, R. Poleski, S. Kozłowski, J. Skowron, D. M. Skowron, K. Rybicki, P. Iwanek, M. Wrona, M. Gromadzki

Abstract: Blue Large-Amplitude Pulsators (BLAPs) form a mysterious class of variable stars with typical periods of tens of minutes and amplitudes above 0.1 mag. In this work, we present results of a variability search focused on timescales shorter than 1 h, conducted in OGLE-IV Galactic disk fields containing about 1.1 billion stellar sources down to I$\approx$20 mag. Twenty-five BLAPs have been detected, 20 of which are new discoveries. Their periods range from 8.4 min to 62.1 min. We have also found six new eclipsing binary systems with orbital periods from 38.3 min to 121.3 min and five short-period large-amplitude (> 0.17 mag in the I-band) variable stars of unknown type.

Authors:K. Thomson-Paressant, C. Neiner, P. Lampens, J. Labadie-Bartz, R. Monier, P. Mathias, A. Tkachenko

Abstract: Numerous candidate hybrid stars of type $\delta$ Scuti - $\gamma$ Doradus have been identified with the Kepler satellite. However, many of them lie outside the theoretically expected instability strip for hybrid pulsation, where $\delta$ Sct and $\gamma$ Dor pulsations can be simultaneously excited. We postulate that some of these pulsating stars may not be genuine hybrid pulsators but rather magnetic $\delta$ Sct stars, for which the rotational modulation from spots on the surface associated to the magnetic field produces frequencies in the same domain as $\gamma$ Dor pulsations. We search for the presence of a magnetic field in a small sample of selected hybrid $\delta$ Sct - $\gamma$ Dor stars using spectropolarimetry. At the time of observations, the only $\delta$ Sct star known to have a magnetic field was HD 188774 with a field strength of a few hundred Gauss. Our observations were thus tailored to detect fields of this typical strength. We find no magnetic field in the hybrid candidate stars we observed. However, two of the three other magnetic $\delta$ Sct stars discovered since these observations have much weaker fields than HD 188774, and are of dynamo origin rather than fossil fields. It is likely that our observations are not sensitive enough to detect such dynamo magnetic fields in the cooler stars of our sample if they are present. This work nevertheless provides reliable upper limits on possible fossil fields in the hotter stars, pointing towards typically weaker fields in $\delta$ Sct stars than in OBA stars in general.

Authors:Thomas Howson, Cosima Breu

Abstract: The large temperature gradients in the solar transition region present a significant challenge to large scale numerical modelling of the Sun's atmosphere. In response, a variety of techniques have been developed which modify the thermodynamics of the system. This sacrifices accuracy in the transition region in favour of accurately tracking the coronal response to heating events. Invariably, the modification leads to an artificial broadening of the transition region. Meanwhile, many contemporary models of the solar atmosphere rely on tracking energy flux from the lower atmosphere, through the transition region and into the corona. In this article, we quantify how the thermodynamic modifications affect the rate of energy injection into the corona. We consider a series of one-dimensional models of atmospheric loops with different numerical resolutions and treatments of the thermodynamics. Then, using Alfv\'en waves as a proxy, we consider how energy injection rates are modified in each case. We find that the thermodynamic treatment and the numerical resolution significantly modify Alfv\'en travel times, the eigenfrequencies and eigenmodes of the system, and the rate at which energy is injected into the corona. Alarmingly, we find that the modification of the energy flux is frequency dependent, meaning that it may be difficult to compare the effects of different velocity drivers on coronal heating if they are imposed below an under-resolved transition region, even if the sophisticated thermodynamic adaptations are implemented.

Authors:A. C. Rubio, A. C. Carciofi, P. Ticiani, B. C. Mota, R. G. Vieira, D. M. Faes, M. Genaro, T. H. de Amorim, R. Klement, I. Araya, C. Arcos, M. Curé, A. Domiciano de Souza, C. Georgy, C. E. Jones, M. W. Suffak, A. C. F. Silva

Abstract: Classical Be stars are fast rotating, near main sequence B-type stars. The rotation and the presence of circumstellar discs profoundly modify the observables of active Be stars. Our goal is to infer stellar and disc parameters, as well as distance and interstellar extinction, using the currently most favoured physical models for these objects. We present BeAtlas, a grid of 61.600 NLTE radiative transfer models for Be stars, calculated with the HDUST code. The grid was coupled with a Monte Carlo Markov chain code to sample the posterior distribution. We test our method on two well-studied Be stars, $\alpha$ Eri and $\beta$ CMi, using photometric, polarimetric and spectroscopic data as input to the code. We recover literature determinations for most of the parameters of the targets, in particular the mass and age of $\alpha$ Eri, the disc parameters of $\beta$ CMi, and their distances and inclinations. The main discrepancy is that we estimate lower rotational rates than previous works. We confirm previously detected signs of disc truncation in $\beta$ CMi and note that its inner disc seems to have a flatter density slope than its outer disc. The correlations between the parameters are complex, further indicating that exploring the entire parameter space simultaneously is a more robust approach, statistically. The combination of BeAtlas and Bayesian-MCMC techniques proves successful, and a powerful new tool for the field: the fundamental parameters of any Be star can now be estimated in a matter of hours or days.

Authors:Chaitanya Prasad Sishtla, Jens Pomoell, Rami Vainio, Emilia Kilpua, Simon Good

Abstract: Alfv\'enic fluctuations of various scales are ubiquitous in the corona, with their non-linear interactions and eventual turbulent cascade resulting in an important heating mechanism that accelerates the solar wind. These fluctuations may be processed by large-scale, transient and coherent heliopsheric structures such as coronal mass ejections (CMEs). In this study we investigate the interactions between Alfv\'enic solar wind fluctuations and CMEs using MHD simulations. We study the transmission of upstream solar wind fluctuations into the CME leading to the formation of CME sheath fluctuations. Additionally, we investigate the influence of the fluctuation frequencies on the extent of the CME sheath. We use an ideal magnetohydrodynamic (MHD) model with an adiabatic equation of state. An Alfv\'en pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components, and a CME is injected by inserting a flux-rope modelled as a magnetic island into the quasi-steady solar wind. The upstream Alfv\'en waves experience a decrease in wavelength and change in the wave vector direction due to the non-radial topology of the CME shock front. The CME sheath inhibits the transmission of high wavelength fluctuations due to the presence of non-radial flows in this region. The frequency of the solar wind fluctuations also affects the steepening of MHD fast waves causing the CME shock propagation speed to vary with the solar wind fluctuation frequencies.

Authors:Madeleine Burheim, Henrik Hartman, Hampus Nilsson

Abstract: Elemental abundances can be determined from stellar spectra, making it possible to study galactic formation and evolution. Accurate atomic data is essential for the reliable interpretation and modeling of astrophysical spectra. In this work, we perform laboratory studies on neutral aluminium. This element is found, for example, in young, massive stars and it is a key element for tracing ongoing nucleosynthesis throughout the Galaxy. The near-infrared (NIR) wavelength region is of particular importance, since extinction in this region is lower than for optical wavelengths. This makes the NIR wavelength region a better probe for highly obscured regions, such as those located close to the Galactic center. We investigate the spectrum of neutral aluminium with the aim to provide oscillator strengths (f-values) of improved accuracy for lines in the NIR and optical regions (670 - 4200 nm). Measurements of high-resolution spectra were performed using a Fourier transform spectrometer and a hollow cathode discharge lamp. The f-values were derived from experimental line intensities combined with published radiative lifetimes. We report oscillator strengths for 12 lines in the NIR and optical spectral regions, with an accuracy between 2 and 11%, as well as branching fractions for an additional 16 lines.

Authors:P. B. Ivanov, J. C. B. Papaloizou

Abstract: We extend our previous work on the evolution of close binary systems with misaligned orbital and spin angular momenta resulting from non-dissipative tidal interaction to include all physical effects contributing to apsidal motion. In addition to tidal distortion of the primary by the compact secondary these include relativistic Einstein precession and the rotational distortion of the primary. The influence of the precession of the line of nodes is included. The dependence of the tidal torque on the apsidal angle $\hat\varpi$ couples the apsidal motion to the rate of evolution of the misalignment angle $\beta$ which is found to oscillate. We provide analytical estimates for the oscillation amplitude $\Delta\beta$ over a wide range of parameter space confirmed by numerical integrations. This is found to be more significant near critical curves on which $d{\hat \varpi } /dt=0$ for a specified $\beta$. We find that to obtain $0.1 < \Delta\beta < \sim 1,$ the mass ratio, $q > \sim1$ the initial eccentricity should be modest, $\cos \beta < 1/\sqrt{5},$ with $\cos\beta <0 $ corresponding to retrograde rotation, initially, and the primary rotation rate should be sufficiently large. The extended discussion of apsidal motion and its coupled evolution to the misalignment angle given here has potential applications to close binaries with anomalous apsidal motion as well as transiting exoplanets such as warm Jupiters.

Authors:Pradeep Kayshap, Peter R. Young

Abstract: The center-to-limb variations (CLV) of Gaussian fit parameters of the transition region Si~{\sc iv} 1402.77~{\AA} spectral line in quiet Sun (QS) and coronal hole (CH) regions are presented. The results are derived from a full-disk mosaic scan obtained by the Interface Region Imaging Spectrograph on 24 September 2017. The CLV for a CH transition region line has not previously been reported, and the parameters are found to show variations consistent with the QS. The intensity increases towards the limb, consistent with an increasing plasma column depth due to line-of-sight effects. The Doppler velocity is normalized to be zero at the limb for both QS and CH and increases to $+4.8$~\kms\ (redshift) at disk center for CH and $+5.2$~\kms\ for QS. Non-thermal broadening in the CH decreases from a maximum of 24~\kms\ at the limb to 10~\kms\ at disk center. For QS the broadening decreases from 25~\kms\ at the limb to 14~\kms\ at disk center. Both Doppler velocities and non-thermal velocities vary linearly with $\cos\,\theta$, where $\theta$ is the heliocentric angle. The QS results for both parameters are consistent with earlier work.

Authors:Pavel Ivanov, John Papaloizou

Abstract: (Abbreviated) We extend the results of our 2021 paper concerning the problem of tidal evolution of a binary system with a rotating primary component with rotation axis arbitrarily inclined with respect to the orbital plane. Only the contribution of quasi-stationary tides is discussed. Unlike previous studies in this field we present evolution equations derived 'from first principles'. The governing equations contain two groups of terms. The first group of terms determines the evolution of orbital parameters and inclination angles a 'viscous' time scale. The second group of terms is due to stellar rotation. These terms are present even when dissipation in the star is neglected. Unlike in our 2021 paper we consider all potentially important sources of apsidal precession in an isolated binary, namely precession arising from the tidal distortion and rotation of the primary as well as Einstein precession. We solve these equations numerically for a sample of input parameters, leaving a complete analysis to an accompanying paper. Periodic changes to both the inclination of the rotational axis and its precession rate are found. For a particular binary parameters periodic flips between prograde and retrograde rotation are possible. Also, when the inclination angle is allowed to vary, libration of the apsidal angle becomes possible. Furthermore, when the spin angular momentum is larger than the orbital angular momentum there is a possibility of a significant periodic eccentricity changes. These phenomena could, in principle, be observed in systems with relatively large inclinations and eccentricities such as e.g. those containing a compact object. In such systems both large inclinations and eccentricities could be generated as a result of a kick applied to the compact object during a supernova explosion.

Authors:Jennifer Anguita-Aguero, Rene A. Mendez, Miguel Videla, Edgardo Costa, Leonardo Vanzi, Nicolas Castro-Morales, Camila Caballero-Valdes

Abstract: We present orbital elements for twenty-two single-line binaries, nine of them studied for the first time, determined from a joint spectroscopic and astrometric solution. The astrometry is based on interferometric measurements obtained with the HRCam Speckle camera on the SOAR 4.1m telescope at Cerro Pachon, Chile, supplemented with historical data. The spectroscopic observations were secured using Echelle spectrographs (FEROS, FIDEOS and HARPS) at La Silla, Chile. A comparison of our orbital elements and systemic velocities with previous studies, including Gaia radial velocities, show the robustness of our estimations. By adopting suitable priors of the trigonometric parallax and spectral type of the primary component, and using a Bayesian inference methodology developed by our group, we were able to estimate mass ratios for these binaries. Combining the present results with a previous study of other single-line from our team we present a pseudo mass-to-luminosity relationship based on twenty three systems (45 stars) in the mass range 0.6 <= M_Sun <= 2.5. We find a reasonable correspondence with a fiducial mass-to-luminosity relationship. We conclude that our methodology does allow to derive tentative mass ratios for this type of binaries.

Authors:Vadim M. Uritsky, Judith T. Karpen, Nour E. Raouafi, Pankaj Kumar, C. Richard DeVore, Craig E. Deforest

Abstract: We present results of a quantitative analysis of structured plasma outflows above a polar coronal hole observed by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory spacecraft. In a 6-hour interval of continuous high-cadence SDO/AIA images, we identified more than 2300 episodes of small-scale plasma flows in the polar corona. The mean upward flow speed measured by the surfing transform technique (Uritsky et al., 2013) is estimated to be 122 $\pm$ 34 \kms, which is comparable to the local sound speed. The typical recurrence period of the flow episodes is 10 to 30 minutes, and the mean duration and transverse size of each episode are about 3-5 min and 3-4 Mm, respectively. The largest identifiable episodes last for tens of minutes and reach widths up to $40$ Mm. For the first time, we demonstrate that the polar coronal-hole outflows obey a family of power-law probability distributions characteristic of impulsive interchange magnetic reconnection. Turbulent photospheric driving may play a crucial role in releasing magnetically confined plasma onto open field. The estimated occurrence rate of the detected self-similar coronal outflows is sufficient for them to make a dominant contribution to the fast-wind mass and energy fluxes and to account for the wind's small-scale structure.

Authors:Yuhao Chen, Zhong Liu, Pengfei Chen, David F. Webb, Qi Hao, Jialiang Hu, Guanchong Cheng, Zhixing Mei, Jing Ye, Qian Wang, Jun Lin

Abstract: A current sheet (CS) is the central structure in the disrupting magnetic configuration during solar eruptions. More than 90\% of the free magnetic energy (the difference between the energy in the non-potential magnetic field and that in the potential one) stored in the coronal magnetic field beforehand is converted into heating and kinetic energy of the plasma, as well as accelerating charged particles, by magnetic reconnection occurring in the CS. However, the detailed physical properties and fine structures of the CS are still unknown since there is no relevant information obtained via in situ detections. The Parker Solar Probe (PSP) may provide us such information should it traverse a CS in the eruption. The perihelion of PSP's final orbit is located at about 10 solar radii from the center of the Sun, so it can observe the CS at a very close distance, or even traverses the CS, which provides us a unique opportunity to look into fine properties and structures of the CS, helping reveal the detailed physics of large-scale reconnection that was impossible before. We evaluate the probability that PSP can traverse a CS, and examine the orbit of a PSP-like spacecraft that has the highest probability to traverse a CS.

Authors:U. Lebreuilly, P. Hennebelle, A. Maury, M. González, A. Traficante, R. Klessen, L. Testi, S. Molinari

Abstract: Context. Due to the presence of magnetic fields, protostellar jets or outflows are a natural consequence of accretion onto protostars. They are expected to play an important role for star and protoplanetary disk formation. Aims. We aim to determine the influence of outflows on star and protoplanetary disk formation in star forming clumps. Methods. Using RAMSES, we perform the first magnetohydrodynamics calculation of massive star-forming clumps with ambipolar diffusion, radiative transfer including the radiative feedback of protostars and protostellar outflows while systematically resolving the disk scales. We compare it to a model without outflows. Results. We find that protostellar outflows have a significant impact on both star and disk formation. They provide additional turbulent and magnetic support to the clump, with typical velocities of a few 10 km/s, impact the disk temperatures, and reduce the accretion rate onto the protostars. While they promote a more numerous stellar population, we do not find that they control the mass scale of the stellar IMF. We find, however, that they have an influence on the high-mass end and the shape of the stellar IMF. Conclusions. Protostellar outflows appear to have a significant influence on both star and disk formation and should therefore be included in realistic simulations of star-forming environments.

Authors:Anisha Sen, S. P. Rajaguru

Abstract: The distribution and evolution of photospheric magnetic field in sunspots, plages and network, and variations in their relative flux content, play key roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra. Differentiating and disentangling such magnetic contributions to RVs help in building models to account for stellar activity signals in high precision RV exoplanet searches. In this work, as earlier authors, we employ high-resolution images of the solar magnetic field and continuum intensities from SDO/HMI to understand the activity contributions to RVs from HARPS-N solar observations. Using well observed physical relationships between strengths and fluxes of photospheric magnetic fields, we show that the strong fields (spots, plages and network) and the weak internetwork fields leave distinguishing features in their contributions to the RV variability. We also find that the fill-factors and average unsigned magnetic fluxes of different features correlate differently with the RVs and hence warrant care in employing either of them as a proxy for RV variations. In addition, we examine disk averaged UV intensities at 1600 \r{A} and 1700 \r{A} wavelength bands imaged by SDO/AIA and their performances as proxies for variations in different magnetic features. We find that the UV intensities provide a better measure of contributions of plage fields to RVs than the Ca II H-K emission indices, especially during high activity levels when the latter tend to saturate.

Authors:M. J. Durbin, R. L. Beaton, A. J. Monson, B. Swidler, J. J. Dalcanton

Abstract: Near-infrared bandpasses on spaceborne observatories diverge from their ground-based counterparts as they are free of atmospheric telluric absorption. Available transformations between respective filter systems in the literature rely on theoretical stellar atmospheres, which are known to have difficulties reproducing observed spectral energy distributions of cool giants. We present new transformations between the 2MASS $JHK_S$ and HST WFC3/IR F110W, F125W, & F160W photometric systems based on synthetic photometry of empirical stellar spectra from four spectral libraries. This sample comprises over 1000 individual stars, which together span nearly the full HR diagram and sample stellar populations from the solar neighborhood out to the Magellanic Clouds, covering a broad range of ages, metallicities, and other relevant stellar properties. In addition to global color-dependent transformations, we examine band-to-band differences for cool, luminous giant stars in particular, including multiple types of primary distance indicators.

Authors:K. Maucó European Southern Observatory, Garching, Germany, C. F. Manara European Southern Observatory, Garching, Germany, M. Ansdell NASA Headquarters, Washington, DC, USA, G. Bettoni Dipartimento di Fisica, Universitá degli Studi di Milano, Milano, Italy Max-Planck Institute for Extraterrestrial Physics, Garching, Germany, R. Claes European Southern Observatory, Garching, Germany, J. Alcala INAF - Osservatorio Astronomico di Capodimonte, Napoli, Italy, A. Miotello European Southern Observatory, Garching, Germany, S. Facchini Dipartimento di Fisica, Universitá degli Studi di Milano, Milano, Italy, T. J. Haworth Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London, UK, G. Lodato Dipartimento di Fisica, Universitá degli Studi di Milano, Milano, Italy, J. P. Williams Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI, USA

Abstract: The evolution of protoplanetary disks is regulated by an interplay of several processes, either internal to the system or related to the environment. As most of the stars and planets have formed in massive stellar clusters, studying the effects of UV radiation on disk evolution is of paramount importance. Here we test the impact of external photoevaporation on the evolution of disks in the $\sigma$ Orionis cluster by conducting the first combined large-scale UV to IR spectroscopic and mm-continuum survey of this region. We study a sample of 50 targets located at increasing distances from the central, OB system $\sigma$ Ori. We combine new VLT/X-Shooter spectra with new and previously published ALMA measurements of disk dust and gas fluxes and masses. We confirm the previously found decrease of $M_{\rm dust}$ in the inner $\sim$0.5 pc of the cluster. This is particularly evident when considering the disks around the more massive stars ($\ge$ 0.4 $M_{\odot}$), where those located in the inner part ($<$ 0.5 pc) have $M_{\rm dust}$ about an order of magnitude lower than the more distant ones. About half of the sample is located in the region of the $\dot{M}_{\rm acc}$ vs $M_{\rm disk}$ expected by models of external photoevaporation, namely showing shorter disk lifetimes. These are observed for all targets with projected separation from $\sigma$ Ori $<$ 0.5 pc, proving that the presence of a massive stellar system affects disk evolution. External photoevaporation is a viable mechanism to explain the observed shorter disk lifetimes and lower $M_{\rm dust}$ in the inner $\sim$0.5 pc of the cluster. Follow-up observations of the low stellar mass targets are crucial to confirm the dependence of the external photoevaporation process with stellar host mass. This work confirms that the effects of external photoevaporation are significant down to impinging radiation as low as $\sim 10^{4}$ G$_0$.

Authors:Nicholas Saunders, Jennifer L. van Saders, Alexander J. Lyttle, Travis S. Metcalfe, Tanda Li, Guy R. Davies, Oliver J. Hall, Warrick H. Ball, Richard Townsend, Orlagh Creevey, Curt Dodds

Abstract: Despite a growing sample of precisely measured stellar rotation periods and ages, the strength of magnetic braking and the degree of departure from standard (Skumanich-like) spindown have remained persistent questions, particularly for stars more evolved than the Sun. Rotation periods can be measured for stars older than the Sun by leveraging asteroseismology, enabling models to be tested against a larger sample of old field stars. Because asteroseismic measurements of rotation do not depend on starspot modulation, they avoid potential biases introduced by the need for a stellar dynamo to drive starspot production. Using a neural network trained on a grid of stellar evolution models and a hierarchical model-fitting approach, we constrain the onset of weakened magnetic braking. We find that a sample of stars with asteroseismically-measured rotation periods and ages is consistent with models that depart from standard spindown prior to reaching the evolutionary stage of the Sun. We test our approach using neural networks trained on model grids produced by separate stellar evolution codes with differing physical assumptions and find that the choices of grid physics can influence the inferred properties of the braking law. We identify the normalized critical Rossby number ${\rm Ro}_{\rm crit}/{\rm Ro}_\odot = 0.91\pm0.03$ as the threshold for the departure from standard rotational evolution. This suggests that weakened magnetic braking poses challenges to gyrochronology for roughly half of the main sequence lifetime of sun-like stars.

Authors:Mami Deka, Shashi M. Kanbur, Sukanta Deb, Susmita Das

Abstract: Pulsating variable $\delta$ Scuti stars are intermediate-mass stars with masses in the range of $1-3$ $M_{\odot}$ and spectral types between $A2$ and $F2$. They can be found at the intersection of the Cepheid instability strip with the main sequence. They can be used as astrophysical laboratories to test theories of stellar evolution and pulsation. In this contribution, we investigate the observed period-colour and amplitude-colour (PCAC) relations at maximum/mean/minimum light of Galactic bulge and Large Magellanic Cloud $\delta$ Scuti stars for the first time and test the hydrogen ionization front (HIF)-photosphere interaction theory using the MESA- RSP code. The PCAC relations, as a function of pulsation phase, are crucial probes of the structure of the outer stellar envelope and provide insight into the physics of stellar pulsation and evolution. The observed behaviour of the $\delta$ Scuti PCAC relations is consistent with the theory of the interaction between the HIF and the stellar photosphere.

Authors:Timo Asikainen, Jani Mantere

Abstract: Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well described by a simple parameterized mathematical expression. We find that the parameters describing even sunspot cycles can be predicted quite accurately using the sunspot number 41 months prior to sunspot minimum as a precursor. We find that the parameters of the odd cycles can be best predicted with maximum geomagnetic aa index close to fall equinox within a 3-year window preceding the sunspot minimum. We use the found precursors to predict all previous sunspot cycles and evaluate the performance with a cross-validation methodology, which indicates that each past cycle is very accurately predicted. For the coming sunspot cycle 25 we predict an amplitude of 171 +/- 23 and the end of the cycle in September 2029 +/- 1.9 years. We are also able to make a rough prediction for cycle 26 based on the predicted cycle 25. While the uncertainty for the cycle amplitude is large we estimate that the cycle 26 will most likely be stronger than cycle 25. These results suggest an increasing trend in solar activity for the next decades.

Authors:Simon Daley-Yates, Moira M. Jardine, Craig D. Johnston

Abstract: Recent observations of rapidly-rotating cool dwarfs have revealed H$\alpha$ line asymmetries indicative of clumps of cool, dense plasma in the stars' coronae. These clumps may be either long-lived (persisting for more than one stellar rotation) or dynamic. The fastest dynamic features show velocities greater than the escape speed, suggesting that they may be centrifugally ejected from the star, contributing to the stellar angular momentum loss. Many however show lower velocities, similar to coronal rain observed on the Sun. We present 2.5D magnetohydrodynamic simulations of the formation and dynamics of these condensations in a rapidly rotating ($P_{\rm rot}~=~ 1 \ \mathrm{day}$) young Sun. Formation is triggered by excess surface heating. This pushes the system out of thermal equilibrium and triggers a thermal instability. The resulting condensations fall back towards the surface. They exhibit quasi-periodic behaviour, with periods longer than typical periods for solar coronal rain. We find line-of-sight velocities for these clumps in the range $50 \ \mathrm{km} \ \mathrm{s}^{-1}$ (blue shifted) to $250 \ \mathrm{km} \ \mathrm{s}^{-1}$ (red shifted). These are typical of those inferred from stellar H$\alpha$ line asymmetries, but the inferred clump masses of $3.6\times 10^{14}\ \mathrm{g}$ are significantly smaller. We find that a maximum of $\simeq~3\%$ of the coronal mass is cool clumps. We conclude that coronal rain may be common in solar like stars, but may appear on much larger scales in rapid rotators.

Authors:William O. Balmer Department of Physics \& Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA Space Telescope Science Institute, Baltimore, MD 21218, USA, Laurent Pueyo Department of Physics \& Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA, Tomas Stolker Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, Sylvestre Lacour LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, Anne-Lise Maire Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, Paul Mollière Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany, Mathias Nowak Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom, David Sing Department of Physics \& Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA Department of Earth \& Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA, Nicolas Pourré European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, Sarah Blunt Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA, Jason J. Wang Center for Interdisciplinary Exploration and Research in Astrophysics, Emily Rickman European Space Agency, Thomas Henning Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, Kim Ward-Duong Department of Astronomy, Smith College, Northampton MA 01063 USA, R. Abuter LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, A. Amorim Universidade de Lisboa - Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, R. Asensio-Torres Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, M. Benisty European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, J. -P. Berger European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, H. Beust European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, A. Boccaletti Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, A. Bohn Space Telescope Science Institute, Baltimore, MD 21218, USA, M. Bonnefoy European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, H. Bonnet LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, G. Bourdarot Max Planck Institute for extraterrestrial Physics, Giessenbachstraße~1, 85748 Garching, Germany European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, W. Brandner Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, F. Cantalloube Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France, P. Caselli CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, B. Charnay Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, G. Chauvin European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, A. Chavez Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA, E. Choquet Max Planck Institute for extraterrestrial Physics, Giessenbachstraße~1, 85748 Garching, Germany, V. Christiaens School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Melbourne, Australia, Y. Clénet Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, V. Coudé du Foresto Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, A. Cridland Space Telescope Science Institute, Baltimore, MD 21218, USA, R. Dembet Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, A. Drescher CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, G. Duvert European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, A. Eckart 1. Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany, F. Eisenhauer CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, H. Feuchtgruber CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, P. Garcia Universidade de Lisboa - Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal, R. Garcia Lopez School of Physics, University College Dublin, Belfield, Dublin 4, Ireland Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, T. Gardner Astronomy Department, University of Michigan, Ann Arbor, MI 48109 USA, E. Gendron Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, R. Genzel CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, S. Gillessen CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, J. H. Girard Department of Physics \& Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA, X. Haubois European Southern Observatory, Casilla 19001, Santiago 19, Chile, G. Heißel Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, S. Hinkley University of Exeter, Physics Building, Stocker Road, Exeter EX4 4QL, United Kingdom, S. Hippler Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, M. Horrobin School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Melbourne, Australia, M. Houllé Max Planck Institute for extraterrestrial Physics, Giessenbachstraße~1, 85748 Garching, Germany, Z. Hubert European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, L. Jocou European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, J. Kammerer Department of Physics \& Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA, M. Keppler Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, P. Kervella Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, L. Kreidberg Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, A. -M. Lagrange European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, V. Lapeyrère Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, J. -B. Le Bouquin European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, P. Léna Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, D. Lutz CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, F. Mang CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, G. -D. Marleau Fakult"at f"ur Physik, Universit"at Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany Instit"ut f"ur Astronomie und Astrophysik, Universit"at T"ubingen, Auf der Morgenstelle 10, 72076 T"ubingen, Germany Center for Space and Habitability, Universit"at Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, A. Mérand LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, J. D. Monnier School of Physics, University College Dublin, Belfield, Dublin 4, Ireland, C. Mordasini Instit"ut f"ur Astronomie und Astrophysik, Universit"at T"ubingen, Auf der Morgenstelle 10, 72076 T"ubingen, Germany, D. Mouillet European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, E. Nasedkin Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France, T. Ott CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, G. P. P. L. Otten Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan, C. Paladini Astronomy Department, University of Michigan, Ann Arbor, MI 48109 USA, T. Paumard Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, K. Perraut European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, G. Perrin Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, O. Pfuhl LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, J. Rameau European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany, L. Rodet Center for Astrophysics and Planetary Science, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA, Z. Rustamkulov Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom, J. Shangguan CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, T. Shimizu CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, C. Straubmeier School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Melbourne, Australia, E. Sturm CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, L. J. Tacconi CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, E. F. van Dishoeck Space Telescope Science Institute, Baltimore, MD 21218, USA CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, A. Vigan Max Planck Institute for extraterrestrial Physics, Giessenbachstraße~1, 85748 Garching, Germany, F. Vincent Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands, F. Widmann CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, E. Wieprecht CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, E. Wiezorrek CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, T. Winterhalder LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, J. Woillez LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France, S. Yazici CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal, A. Young CENTRA - Centro de Astrof\' isica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal

Abstract: Tension remains between the observed and modeled properties of substellar objects, but objects in binary orbits, with known dynamical masses can provide a way forward. HD 72946 B is a recently imaged brown dwarf companion to the nearby, solar type star. We achieve $\sim100~\mu\mathrm{as}$ relative astrometry of HD 72946 B in the K-band using VLTI/GRAVITY, unprecedented for a benchmark brown dwarf. We fit an ensemble of measurements of the orbit using orbitize! and derive a strong dynamical mass constraint $\mathrm{M_B}=69.5\pm0.5~\mathrm{M_{Jup}}$ assuming a strong prior on the host star mass $\mathrm{M_A}=0.97\pm0.01~\mathrm{M_\odot}$ from an updated stellar analysis. We fit the spectrum of the companion to a grid of self-consistent BT-Settl-CIFIST model atmospheres, and perform atmospheric retrievals using petitRADTRANS. A dynamical mass prior only marginally influences the sampled distribution on effective temperature, but has a large influence on the surface gravity and radius, as expected. The dynamical mass alone does not strongly influence retrieved pressure-temperature or cloud parameters within our current retrieval setup. Independent of cloud prescription and prior assumptions, we find agreement within $\pm2\,\sigma$ between the C/O ratio of the host ($0.52\pm0.05)$ and brown dwarf ($0.43$ to $0.63$), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high ($0.6-0.8$) in light of an excellent agreement of the data with the solar abundance model grid. Future work on our retrieval framework will seek to resolve this tension. Additional study of low surface-gravity objects is necessary to assess the influence of a dynamical mass prior on atmospheric analysis.

Authors:D. Nandal, E. Farrell, G. Buldgen, G. Meynet, S. Ekstrom

Abstract: We present evolutionary models of massive, accreting population III stars with constant and variable accretion rates until the end of silicon burning, with final masses of 1000 - 3000 Msol. In all our models, after the core-hydrogen burning phase, the star expands towards the red side of the Hertzsprung-Russell diagram where it spends the rest of its evolution. During core helium burning, the models exhibit an outer convective envelope as well as many large intermediate convective zones. These intermediate zones allow for strong internal mixing to occur which enriches the surface in helium. The effect of increasing metallicity at a constant accretion rate of 1e-3 Msol/yr shows an increase in lifetime, final mass and distribution of helium in the envelope. Our fiducial model with mass of 3000 Msol has a final surface helium abundance of 0.74 with 9% of its total mass or 50% of the core mass below Gamma1 < 4/3 at the end of core silicon burning. If the collapse of the core is accompanied by the ejection of the envelope above the carbon-oxygen core, this could have a significant impact on the chemical evolution of the surroundings and subsequent stellar generations. The model has has a final log(N/O) ~ 0.45, above the lower limit in the recently detected high-redshift galaxy GN-z11. We discuss the impact of a single 3000 Msol on chemical, mechanical and radiative feedback, and present directions for future work.

Authors:M. Laversveiler, D. R. Gonçalves

Abstract: Here we study the symbiotic stars (SySt) population and its relation with type Ia supernovae (SNe Ia) in the galaxies of the Local Group. SySt are low- and/or intermediate-mass evolved binary systems where a white dwarf (WD) accretes mass from a giant star. A fraction of these WDs can become massive enough to reach the Chandrasekhar mass. Therefore, SySt have been considered as potential SNe Ia progenitors. Taking two approaches, one empirical and another statistical, we estimated the SySt population on the Galaxy as having a minimum value of $1.69\times10^3$ and a expected one of $3.23\times10^4$. For Local Group dwarfs galaxies, the computed SySt population ranges from 2 to 4 orders of magnitudes lower. Concerning the SNe Ia with SySt progenitors, our general result is that SySt are not the main SNe Ia progenitors. On the other hand, we still expect that about 0.5-8% of the SNe Ia have symbiotic progenitors in the Milky Way, while the majority of the - low-mass - dwarfs galaxies did not experience a symbiotic type Ia supernova.

Authors:Chenyu He, Chengyuan Li, Weijia Sun, Richard de Grijs, Lu Li, Jing Zhong, Songmei Qin, Li Chen, Li Wang, Baitian Tang, Zhengyi Shao, Cheng Xu

Abstract: The split main sequences found in the colour-magnitude diagrams of star clusters younger than ~600 Myr are suggested to be caused by the dichotomy of stellar rotation rates of upper main-sequence stars. Tidal interactions have been suggested as a possible explanation of the dichotomy of the stellar rotation rates. This hypothesis proposes that the slow rotation rates of stars along the split main sequences are caused by tidal interactions in binaries. To test this scenario, we measured the variations in the radial velocities of slowly rotating stars along the split main sequence of the young Galactic cluster NGC 2422 (~90 Myr) using spectra obtained at multiple epochs with the Canada-France-Hawai'i Telescope. Our results show that most slowly rotating stars are not radial-velocity variables. Using the theory of dynamical tides, we find that the binary separations necessary to fully or partially synchronise our spectroscopic targets, on time-scales shorter than the cluster age, predict much larger radial velocity variations across multiple-epoch observations, or a much larger radial velocity dispersion at a single epoch, than the observed values. This indicates that tidal interactions are not the dominant mechanism to form slowly rotating stars along the split main sequences. As the observations of the rotation velocity distribution among B- and A-type stars in binaries of larger separations hint at a much stronger effect of braking with age, we discuss the consequences of relaxing the constraints of the dynamical tides theory.

Authors:Ananya Rawat, Girjesh Gupta

Abstract: Coronal fan loops rooted in sunspot umbra show outward propagating waves with subsonic phase speed and period around 3-min. However, their source region in the lower atmosphere is still ambiguous. We performed multi-wavelength observations of a clean fan loop system rooted in sunspot observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We utilised less explored property of frequency modulation of these 3-min waves from the photosphere to corona, and found them to be periodic with the ranges in 14-20 min, and 24-35 min. Based on our findings, we interpret that 3-min slow waves observed in the coronal fan loops are driven by 3-min oscillations observed at the photospheric footpoints of these fan loops in the umbral region. We also explored any connection between 3-min and 5-min oscillations observed at the photosphere, and found them to be poorly understood. Results provide clear evidence of magnetic coupling of the solar umbral atmosphere through propagation of 3-min waves along the fan loops at different atmospheric heights.

Authors:A. A. Vidotto, V. Bourrier, R. Fares, S. Bellotti, J. F. Donati, P. Petit, G. A. J. Hussain, J. Morin

Abstract: The M dwarf star GJ 436 hosts a warm-Neptune that is losing substantial amount of atmosphere, which is then shaped by the interactions with the wind of the host star. The stellar wind is formed by particles and magnetic fields that shape the exo-space weather around the exoplanet GJ 436 b. Here, we use the recently published magnetic map of GJ 436 to model its 3D Alfv\'en-wave driven wind. By comparing our results with previous transmission spectroscopic models and measurements of non-thermal velocities at the transition region of GJ 436, our models indicate that the wind of GJ 436 is powered by a smaller flux of Alfv\'en waves than that powering the wind of the Sun. This suggests that the canonical flux of Alfv\'en waves assumed in solar wind models might not be applicable to the winds of old M dwarf stars. Compared to the solar wind, GJ 436's wind has a weaker acceleration and an extended sub-Alfv\'enic region. This is important because it places the orbit of GJ 436 b inside the region dominated by the stellar magnetic field (i.e., inside the Alfv\'en surface). Due to the sub-Alfv\'enic motion of the planet through the stellar wind, magnetohydrodynamic waves and particles released in reconnection events can travel along the magnetic field lines towards the star, which could power the anomalous ultraviolet flare distribution recently observed in the system. For an assumed planetary magnetic field of $B_p \simeq 2$ G, we derive the power released by stellar wind-planet interactions as $\mathcal{P} \sim 10^{22}$ -- $10^{23}$ erg s$^{-1}$, which is consistent with the upper limit of $10^{26}$ erg s$^{-1}$ derived from ultraviolet lines. We further highlight that, because star-planet interactions depend on stellar wind properties, observations that probe these interactions and the magnetic map used in 3D stellar wind simulations should be contemporaneous for deriving realistic results.

Authors:Yael Naze ULiege, Gregor Rauw ULiege, Rachel Johnson Univ Denver, Eric Gosset ULiege, Jennifer L. Hoffman Univ Denver

Abstract: WR21 and WR31 are two WR+O binaries with short periods, quite similar to the case of V444 Cyg. The XMM-Newton observatory has monitored these two objects and clearly revealed phase-locked variations as expected from colliding winds. The changes are maximum in the soft band (0.5--2.keV, variations by a factor 3--4) where they are intrinsically linked to absorption effects. The increase in absorption due to the dense WR wind is confirmed by the spectral analysis. The flux maximum is however not detected exactly at conjunction with the O star in front but slightly afterwards, suggesting Coriolis deflection of the collision zone as in V444 Cyg. In the hard band (2.--10. keV), the variations (by a factor of 1.5--2.0) are much more limited. Because of the lower orbital inclinations, eclipses as observed for V444 Cyg are not detected in these systems.

Authors:Anne Rathsam, Jorge Meléndez, Gabriela Carvalho Silva

Abstract: The main goal of this work is to evaluate the correlation between Li abundance, age, and mass. Using high-quality ESO/HARPS data (R $\simeq$ 115 000; 270 $\leq$ SNR $\leq$ 1000), we measured Li abundances via spectral synthesis of the 6707.8 \r{A} $^7$Li line in 74 solar twins and analogs. Our joint analysis of 151 Sun-like stars (72 from our sample plus 79 solar twins from a previous study) confirms the strong Li abundance-age correlation reported by other works. Mass and convective envelope size also seem to be connected with Li abundance but with lower significance. We have found a link between the presence of planets and low Li abundances in a sample of 192 stars with a high significance. Our results agree qualitatively with non-standard models, and indicate that several extra transport mechanisms must be taken into account to explain the behaviour of Li abundance for stars with different masses and ages.

Authors:J. R. Maund

Abstract: The measurement of non-zero polarization can be used to infer the presence of departures from spherical symmetry in supernovae (SNe). The origin of the majority of the intrinsic polarization observed in SNe is in electron scattering, which induces a wavelength-independent continuum polarization that is generally observed to be low (<1%) for all SN types. The key indicator of asymmetry in SNe is the polarization observed across spectral lines, in particular the characteristic ``inverse P Cygni'' profile. The results of a suite of 900 Monte Carlo radiative transfer simulations are presented here. These simulations cover a range of possible axisymmetric structures (including unipolar, bipolar and equatorial enhancements) for the line forming region of the Ca II infrared triplet. Using a Variational Autoencoder, 7 key latent parameters are learned that describe the relationship between Stokes I and Stokes q, under the assumption of an axially symmetric line forming region and resonant scattering. Likelihood-free inference techniques are used to invert the Stokes I and q line profiles, in the latent space, to derive the underlying geometries. For axially symmetric structures, that yield an observable ``dominant axis'' on the Stokes $q-u$ plane, we propose the existence of a geometry ``conjugate" (which is indistinguishable under a rotation of $\pi /2$). Using this machine learning infrastructure, we attempt to identify possible geometries associated with spectropolarimetric observations of the Type Ib SN 2017gax.

Authors:Kathryn Lester, Steve Howell, Rachel Matson, Elise Furlan, Crystal Gnilka, Colin Littlefield, David Ciardi, Mark Everett, Sergio Fajardo-Acosta, Catherine Clark

Abstract: Roughly half of Solar-type planet hosts have stellar companions, so understanding how these binary companions affect the formation and evolution of planets is an important component to understanding planetary systems overall. Measuring the dynamical properties of planet host binaries enables a valuable test of planet formation in multi-star systems and requires knowledge of the binary orbital parameters. Using high resolution imaging, we have measured the relative astrometry and visual orbits of 13 binary systems where one of the stars is known to host a transiting exoplanet. Our results indicate that the mutual inclination between the orbits of the binary hosts and the transiting planets are well aligned. Our results for close binary systems (a<100 AU) complement past work for wide planet host binaries from Gaia.

Authors:Sunayana Maben, Simon W. Campbell, Yerra Bharat Kumar, Bacham E. Reddy, Gang Zhao

Abstract: Carbon-deficient red giants (CDGs) are a peculiar class of stars that have eluded explanation for decades. We aim to better characterise CDGs by using asteroseismology (Kepler, TESS) combined with spectroscopy (APOGEE, LAMOST), and astrometry (Gaia). We discovered 15 new CDGs in the Kepler field, and confirm that CDGs are rare, being only $0.15\%$ of our background sample. Remarkably, we find that our CDGs are almost exclusively in the red clump (RC) phase. Asteroseismic masses reveal that our CDGs are primarily low-mass stars ($M \lesssim$ 2~M$_{\odot}$), in contrast to previous studies which suggested they are intermediate mass ($M = 2.5 - 5.0~\rm M_{\odot}$) based on HR diagrams. A very high fraction of our CDGs ($50\%$) are also Li-rich giants. We observe a bimodal distribution of luminosity in our CDGs, with one group having normal RC luminosity and the other being a factor of two more luminous than expected for their masses. We find demarcations in chemical patterns and luminosities which lead us to split them into three groups: (i) normal-luminosity CDGs, (ii) over-luminous CDGs, and (iii) over-luminous highly-polluted CDGs. We conclude that a merger of a helium white dwarf with an RGB star is the most likely scenario for the two groups of over-luminous stars. Binary mass-transfer from intermediate-mass AGB stars is a possibility for the highly-polluted over-luminous group. For the normal-luminosity CDGs, we cannot distinguish between core He-flash pollution or lower-mass merger scenarios. Due to the overlap with the CDGs, Li-rich giants may have similar formation channels.

Authors:Michaela Brchnelova, Błażej Kuźma, Fan Zhang, Andrea Lani, Stefaan Poedts

Abstract: The global coronal model COCONUT was originally developed to replace models such as the WSA model in space weather forecasting to improve the physical accuracy of the predictions. This model has, however, several simplifications implemented in its formulation to allow for rapid convergence, one of which includes a single-fluid treatment. In this paper, we have two goals. Firstly, we aim to introduce a novel multi-fluid global coronal model and validate it with simple cases as well as with real data-driven applications. Secondly, we aim to investigate to what extent considering a single-fluid plasma in the global coronal model might affect the resulting plasma dynamics, and thus whether the assumptions on which the single-fluid coronal model is based are justified. We developed a multi-fluid global coronal model, COCONUT-MF, which resolves the ion and neutral fluid equations separately. While this model is still steady-state and thus does not resolve unsteady processes, it can account for charge exchange, chemical and collisional contributions. We present the results of the ion-neutral modelling for a dipole, a minimum of solar activity, and a solar maximum. We demonstrate the higher accuracy of the applied AUSM+ scheme compared to HLL. Subsequently, we also evaluate the effects of the considered ion-neutral coupling terms on the resulting plasma dynamics. Despite the very low concentration of neutrals, these terms still affect the flow field to a limited but non-negligible extent (up to 5 to 10% locally). Even though the coronal plasma is generally assumed to be collisionless, our results show that there is sufficient collisionality in it to couple the two fluids. Follow-up work will include extension of the model to lower atmospheric layers of the Sun and inclusion of more advanced physical terms such as heating and radiation.

Authors:Antonio Martínez-Henares, Izaskun Jiménez-Serra, Jesús Martín-Pintado, Nuria Huélamo, Sirina Prasad, Qizhou Zhang, James Moran, Yue Cao, Alejandro Báez-Rubio

Abstract: MWC 349A is a massive star with a well-known circumstellar disk rotating following a Keplerian law, and an ionized wind launched from the disk surface. Recent ALMA observations carried out toward this system have however revealed an additional high-velocity component in the strong, maser emission of hydrogen radio recombination lines (RRLs), suggesting the presence of a high-velocity ionized jet. In this work, we present 3D non-LTE radiative transfer modeling of the emission of the H30$\alpha$ and H26$\alpha$ maser lines, and of their associated radio continuum emission, toward the MWC 349A massive star. By using the MORELI code, we reproduce the spatial distribution and kinematics of the high-velocity emission of the H30$\alpha$ and H26$\alpha$ maser lines with a high-velocity ionized jet expanding at a velocity of $\sim$ 250 km s$^{-1}$, surrounded by MWC 349A's wide-angle ionized wind. The bipolar jet, which is launched from MWC 349A's disk, is poorly collimated and slightly miss-aligned with respect to the disk rotation axis. Thanks to the unprecedented sensitivity and spatial accuracy provided by ALMA, we also find that the already known, wide-angle ionized wind decelerates as it expands radially from the ionized disk. We briefly discuss the implications of our findings in understanding the formation and evolution of massive stars. Our results show the huge potential of RRL masers as powerful probes of the innermost ionized regions around massive stars and of their high-velocity jets.

Authors:Albert Bruch

Abstract: Continuing previous work on the identification and characterization of periodic and non-periodic variations in long and almost uninterrupted high cadence light curves of cataclysmic variables observed by the TESS mission, the results on 23 novalike variables and old novae out of sample of 127 suchsystems taken from the Ritter & Kolb catalogue are presented. All of them exhibit at least at some epochs either positive or negative (or both) superhumps, and in 19 of them superhumps were detected for the first time. The basic properties of the superhumps such as their periods, their appearance and disappearance, and their waveforms are explored. Together with recent reports in the literature, this elevates the number of known novalike variables and old novae with superhumps by more than 50%. The previous census of superhumps and the Stolz-Schoembs relation for these stars are updated. Attention is drawn to superhump properties in some stars which behave differently from the average, as well as to positive superhumps in high mass ratio systems which defy theory. As a byproduct, the orbital periods of 13 stars are either improved or newly measured, correcting previously reported erroneous values.

Authors:Kiera van der Sande, Andrés Muñoz-Jaramillo, Subhamoy Chatterjee

Abstract: Solar flare forecasting research using machine learning (ML) has focused on high resolution magnetogram data from the SDO/HMI era covering Solar Cycle 24 and the start of Solar Cycle 25, with some efforts looking back to SOHO/MDI for data from Solar Cycle 23. In this paper, we consider over 4 solar cycles of daily historical magnetogram data from multiple instruments. This is the first attempt to take advantage of this historical data for ML-based flare forecasting. We apply a convolutional neural network (CNN) to extract features from full-disk magnetograms together with a logistic regression model to incorporate scalar features based on magnetograms and flaring history. We use an ensemble approach to generate calibrated probabilistic forecasts of M-class or larger flares in the next 24 hours. Overall, we find that including historical data improves forecasting skill and reliability. We show that single frame magnetograms do not contain significantly more relevant information than can be summarized in a small number of scalar features, and that flaring history has greater predictive power than our CNN-extracted features. This indicates the importance of including temporal information in flare forecasting models.

Authors:Paola Testa Harvard-Smithsonian Center for Astrophysics, Helle Bakke Rosseland Centre for Solar Physics, University of Oslo Institute of Theoretical Astrophysics, University of Oslo, Luc Rouppe van der Voort Rosseland Centre for Solar Physics, University of Oslo Institute of Theoretical Astrophysics, University of Oslo, Bart De Pontieu Lockheed Martin Solar & Astrophysics Laboratory Rosseland Centre for Solar Physics, University of Oslo Institute of Theoretical Astrophysics, University of Oslo

Abstract: High resolution spectral observations of the lower solar atmosphere (chromosphere and transition region) during coronal heating events, in combination with predictions from models of impulsively heated loops, provide powerful diagnostics of the properties of the heating in active region cores. Here we analyze the first coordinated observations of such events with the Interface Region Imaging Spectrograph (IRIS) and the CHROMospheric Imaging Spectrometer (CHROMIS), at the Swedish 1-m Solar Telescope (SST), which provided extremely high spatial resolution and revealed chromospheric brightenings with spatial dimensions down to ~150km. We use machine learning methods (k-means clustering) and find significant coherence in the spatial and temporal properties of the chromospheric spectra, suggesting, in turn, coherence in the spatial and temporal distribution of the coronal heating. The comparison of IRIS and CHROMIS spectra with simulations suggest that both non-thermal electrons with low energy (low-energy cutoff ~5keV) and direct heating in the corona transported by thermal conduction contribute to the heating of the low atmosphere. This is consistent with growing evidence that non-thermal electrons are not uncommon in small heating events (nano- to micro-flares), and that their properties can be constrained by chromospheric and transition region spectral observations.

Authors:Pascale Garaud, Saniya Khan, Justin M. Brown

Abstract: Shear instabilities can be the source of significant amounts of turbulent mixing in stellar radiative zones. Past attempts at modeling their effects (either theoretically or using numerical simulations) have focused on idealized geometries where the shear is either purely vertical or purely horizontal. In stars, however, the shear can have arbitrary directions with respect to gravity. In this work, we use direct numerical simulations to investigate the nonlinear saturation of shear instabilities in a stably stratified fluid, where the shear is sinusoidal in the horizontal direction, and either constant or sinusoidal in the vertical direction. We find that, in the parameter regime studied here (non-diffusive, fully turbulent flow), the mean vertical shear does not play any role in controlling the dynamics of the resulting turbulence unless its Richardson number is smaller than one (approximately). As most stellar radiative regions have a Richardson number much greater than one, our result implies that the vertical shear can essentially be ignored in the computation of the vertical mixing coefficient associated with shear instabilities for the purpose of stellar evolution calculations, even when it is much larger than the horizontal shear (as in the solar tachocline, for instance).

Authors:H. Netzel, L. Molnar, M. Joyce

Abstract: Photometric observations from the last decade have revealed additional low-amplitude periodicities in many classical pulsators that are likely due to pulsations in non-radial modes. One group of multi-mode RR Lyrae stars, the so-called 0.61 stars, is particularly interesting. In these stars, the radial first overtone is accompanied by additional signals with period ratios around 0.61. The most promising explanation for these signals is pulsation in non-radial modes of degrees 8 and 9. If the theory behind the additional signals in the 0.61 stars is substantiated, it would allow us to use non-radial modes to study classical pulsators. We aim to perform asteroseismic modeling of selected 0.61 stars with independently determined physical parameters to test whether this assumption behind the modeling leads to correct results. Namely, we test whether the additional signals are indeed due to non-radial modes of the proposed moderate degrees. We selected a number of and RR Lyrae stars that are also 0.61 stars and have good observational constraints on their other physical parameters. We assume that the nature of those modes is correctly explained with non-radial modes of degrees 8 or 9. Using this assumption and observational constraints on physical parameters, we performed asteroseismic modeling to test whether the observed periods and period ratios can be reproduced. For the majority of selected targets, we obtained a good match between observed and calculated periods and period ratios. For a few targets however, the results obtained are ambiguous and not straightforward to interpret.

Authors:T. Steinmetz Nicolaus Copernicus Astronomical Center, T. Kamiński Nicolaus Copernicus Astronomical Center, M. Schmidt Nicolaus Copernicus Astronomical Center, A. Kiljan Faculty of Physics, University of Warsaw

Abstract: Context. V1309 Sco is an example of a red nova, a product of the merger between non-compact stars. V1309 Sco is particularly important within the class of red novae due to the abundance of the progenitor binary before the merger. Aims. We aim to investigate the spatio-kinematic and chemical properties of the circumstellar environment, including deriving the physical conditions and establishing the origins of the different circumstellar components. Methods. We use radioactive transfer modelling of molecular emission in sub-mm spectra to examine the properties of the molecular gas, and use forbidden line diagnostics from optical spectra to constrain electron density and temperature using forbidden line diagnostics. We compare line intensities from shock models to observations to look for and constrain shocks. Results. We derive a new kinematical distance of 5.6 kpc to the source. The detection of ro-vibrational H2 and sub-mm HCO+ emission in 2016 and 2019, respectively, indicate active shock interactions within the circumstellar environment. The velocity profiles of both H2 and HCO+, as well as the moment-1 maps of sub-mm CO and 29-SiO, indicate a bipolar structure that may be asymmetric. The sub-mm and optical molecular emission exhibits temperatures of 35-113 and 200 K, respectively, whilst the atomic gas is much hotter, with temperatures of 5-15 kK, which may be due to shock heating. Conclusions. The detection of a bipolar structure in V1309 Sco indicates further similarities with the structure of another Galactic red nova, V4332 Sgr. It provides evidence that bipolar structures may be common in red novae. All collected data are consistent with V1309 Sco bring a kinematically and chemically complex system.

Authors:Gregory J. Herczeg, Yuguang Chen, Jean-Francois Donati, Andrea K. Dupree, Frederick M. Walter, Lynne A. Hillenbrand, Christopher M. Johns-Krull, Carlo F. Manara, Hans Moritz Guenther, Min Fang, P. Christian Schneider, Jeff A. Valenti, Silvia H. P. Alencar, Laura Venuti, Juan Manuel Alcala, Antonio Frasca, Nicole Arulanantham, Jeffrey L. Linsky, Jerome Bouvier, Nancy S. Brickhouse, Nuria Calvet, Catherine C. Espaillat, Justyn Campbell-White, John M. Carpenter, Seok-Jun Chang, Kelle L. Cruz, S. E. Dahm, Jochen Eisloeffel, Suzan Edwards, William J. Fischer, Zhen Guo, Thomas Henning, Tao Ji, Jesse Jose, Joel H. Kastner, Ralf Launhardt, David A. Principe, Conner E. Robinson, Javier Serna, Michal Siwak, Michael F. Sterzik, Shinsuke Takasao

Abstract: Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998--2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of $2.51\times10^{-9}$~M$_\odot$~yr$^{-1}$ and a Gaussian distribution with a FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Ly$\alpha$. The accretion luminosities are well correlated with He line luminosities but poorly correlated with H$\alpha$ and H$\beta$ luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars.

Authors:David M. Long, Lucie M. Green, Francesco Pecora, David H. Brooks, Hanna Strecker, David Orozco-Suárez, Laura A. Hayes, Emma E. Davies, Ute V. Amerstorfer, Marilena Mierla, David Lario, David Berghmans, Andrei N. Zhukov, Hannah T. Rüdisser

Abstract: Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope's handedness and the number of turns that any helical field lines make is difficult without magnetic field modelling or in-situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 4 and 5 September 2022 made using the \textit{Solar Orbiter} spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within $\sim$5~hours of the second plasma flow. The erupting flux rope then passed over the \textit{Parker Solar Probe} spacecraft during its Encounter 13, enabling \textit{in-situ} diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the \textit{in-situ} measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun.

Authors:Dominic M. Bowman, Jennifer van Saders, Jorick S. Vink

Abstract: In this introductory chapter of the Special Issue entitled `The Structure and Evolution of Stars', we highlight the recent major progress made in our understanding in the physics that governs stellar interiors. In so doing, we combine insight from observations, 1D evolutionary modelling and 2+3D rotating (magneto)hydrodynamical simulations. Therefore, a complete and compelling picture of the necessary ingredients in state-of-the-art stellar structure theory and areas in which improvements still need to be made are contextualised. Additionally, the over-arching perspective that links all the themes of subsequent chapters is presented.

Authors:G. Buldgen, A. Noels, V. A. Baturin, A. V. Oreshina, S. V. Ayukov, R. Scuflaire, A. M. Amarsi, N. Grevesse

Abstract: Context. The metal mass fraction of the Sun Z is a key constraint in solar modelling, but its value is still under debate. The standard solar chemical composition of the late 2000s have the ratio of metals to hydrogen Z/X = 0.0181, with a small increase to 0.0187 in 2021, as inferred from 3D non-LTE spectroscopy. However, more recent work on a horizontally and temporally averaged <3D> model claim Z/X = 0.0225, consistent with the high values of twenty-five years ago based on 1D LTE spectroscopy. Aims. We aim to determine a precise and robust value of the solar metal mass fraction from helioseismic inversions, thus providing independent constraints from spectroscopic methods. Methods. We devise a detailed seismic reconstruction technique of the solar envelope, combining multiple inversions and equations of state to accurately and precisely determine the metal mass fraction value. Results. We show that a low value of the solar metal mass fraction corresponding to Z/X = 0.0187 is favoured by helioseismic constraints and that a higher metal mass fraction corresponding to Z/X = 0.0225 are strongly rejected by helioseismic data. Conclusions. We conclude that direct measurement of the metal mass fraction in the solar envelope favours a low metallicity, in line with the 3D non-LTE spectroscopic determination of 2021. A high metal mass fraction as measured using a <3D> model in 2022 is disfavoured by helioseismology for all modern equations of state used to model the solar convective envelope.

Authors:Erin Motherway, Aaron M. Geller, Anna C. Childs, Claire Zwicker, Ted von Hippel

Abstract: M35 is a young open cluster and home to an extensive binary population. Using Gaia DR3, Pan-STARRS, and 2MASS photometry with the Bayesian statistical software, BASE-9, we derive precise cluster parameters, identify single and binary cluster members, and extract their masses. We identify 571 binaries down to Gaia G = 20.3 and a lower-limit on the binary frequency of f_b = 0.41 +/- 0.02. We extend the binary demographics by many magnitudes faint-ward of previous (radial-velocity) studies of this cluster and further away from the cluster center (1.78-degrees, roughly 10 core radii). We find the binary stars to be more centrally concentrated than the single stars in the cluster. Furthermore, we find strong evidence for mass segregation within the binary population itself, with progressively more massive binary samples becoming more and more centrally concentrated. For the single stars, we find weaker evidence for mass segregation; only the most massive single stars (> 2.5MSun) appear more centrally concentrated. Given the cluster age of ~200 Myr, and our derived half-mass relaxation time for the cluster of 230 +/- 84 Myr, we estimate ~47% of the binary stars and ~12% of single stars in the cluster have had time to become dynamically mass segregated. Importantly, when we investigate only stars with mass segregation timescales greater than the cluster age, we still find the binaries to be more centrally concentrated than the singles, suggesting the binaries may have formed with a primordially different spatial distribution than the single stars.

Authors:Richa N. Jain, R. K. Choudhary, Anil Bhardwaj, T. Imamura, Anshuman Sharma, Umang M. Parikh

Abstract: The solar inner corona is a region that plays a critical role in energizing the solar wind and propelling it to supersonic and supra-Alfvenic velocities. Despite its importance, this region remains poorly understood because of being least explored due to observational limitations. The coronal radio sounding technique in this context becomes useful as it helps in providing information in parts of this least explored region. To shed light on the dynamics of the solar wind in the inner corona, we conducted a study using data obtained from coronal radio-sounding experiments carried out by the Akatsuki spacecraft during the 2021 Venus-solar conjunction event. By analyzing X-band radio signals recorded at two ground stations (IDSN in Bangalore and UDSC in Japan), we investigated plasma turbulence characteristics and estimated flow speed measurements based on isotropic quasi-static turbulence models. Our analysis revealed that the speed of the solar wind in the inner corona (at heliocentric distances from 5 to 13 solar radii), ranging from 220-550 km/sec, was higher than the expected average flow speeds in this region. By integrating our radio-sounding results with EUV images of the solar disk, we gained a unique perspective on the properties and energization of high-velocity plasma streams originating from coronal holes. We tracked the evolution of fast solar wind streams emanating from an extended coronal hole as they propagated to increasing heliocentric distances. Our study provides unique insights into the least-explored inner coronal region by corroborating radio sounding results with EUV observations of the corona.

Authors:Mayank Narang, Manoj Puravankara, Himanshu Tyagi, Prasanta K. Nayak, Saurabh Sharma, Arun Surya, Bihan Banerjee, Blesson Mathew, Arpan Ghosh, Aayushi Verma

Abstract: Optical spectroscopy offers the most direct view of the stellar properties and the accretion indicators. Standard accretion tracers, such as $H\beta$, $H\alpha$, and, Ca II triplet lines, and most photospheric features, fall in the optical wavelengths. However, these tracers are not readily observable from deeply embedded protostars because of the large line of sight extinction (Av $\sim$ 50-100 mag) toward them. In some cases, however, it is possible to observe protostars at optical wavelengths if the outflow cavity is aligned along the line-of-sight that allows observations of the photosphere, or the envelope is very tenuous and thin such that the extinction is low. In such cases, we can not only detect these protostars at optical wavelengths but also follow up spectroscopically. We have used the HOPS catalog (Furlan et al. 2016) of protostars in Orion to search for optical counterparts for protostars in the Gaia DR3 survey. Out of the 330 protostars in the HOPS sample, an optical counterpart within 2" is detected for 62 of the protostars. For 17 out of 62 optically detected protostars, we obtained optical spectra { (between 5500 to 8900 $\AA$) using the Aries-Devasthal Faint Object Spectrograph \& Camera (ADFOSC) on the 3.6-m Devasthal Optical Telescope (DOT) and Hanle Faint Object Spectrograph Camera (HFOSC) on 2-m Himalayan Chandra Telescope (HCT)}. We detect strong photospheric features, such as the TiO bands in the spectra {(of 4 protostars)}, hinting that photospheres can form early on in the star formation process. We further determined the spectral types of protostars, which show photospheres similar to a late M-type. Mass accretion rates derived for the protostars are similar to those found for T-Tauri stars, in the range of 10$^{-7}$ to 10$^{-8}$ $M_\odot$/yr.

Authors:K. Brogaard, T. Arentoft, A. Miglio, G. Casali, J. S. Thomsen, M. Tailo, J. Montalbán, V. Grisoni, E. Willett, A. Stokholm, F. Grundahl, D. Stello, E. L. Sandquist

Abstract: Asteroseismology of solar-like oscillations in giant stars allow the derivation of their masses and radii. For members of open clusters this allows an age estimate of the cluster which should be identical to the age estimate from the colour-magnitude diagram, but independent of the uncertainties that are present for that type of analysis. Thus, a more precise and accurate age estimate can be obtained. We aim to measure asteroseismic properties of oscillating giant members of the open cluster NGC 6866 and utilise these for a cluster age estimate. Model comparisons allow constraints on the stellar physics, and here we investigate the efficiency of convective-core overshoot and effects of rotation during the main-sequence, which has a significant influence on the age for these relatively massive giants. We identify six giant members of NGC 6866 and derive asteroseismic measurements for five of them. This constrains the convective-core overshoot and enables a more precise and accurate age estimate than previously possible. Asteroseismology establishes the helium-core burning evolutionary phase for the giants, which have a mean mass of 2.8 $M_{\odot}$. Their radii are significantly smaller than predicted by current 1D stellar models unless the amount of convective-core overshoot on the main sequence is reduced to $\alpha_{ov} \leq 0.1 H_p$ in the step-overshoot description. Our measurements also suggest that rotation has affected the evolution of the stars in NGC 6866 in a way that is consistent with 3D simulations but not with current 1D stellar models. The cluster age is estimated to be 0.43 $\pm$ 0.05 Gyr, significantly younger and more precise than most previous estimates. We derive a precise cluster age while constraining convective-core overshooting and effects of rotation in the models. We uncover potential biases for automated age estimates of helium-core burning stars.

Authors:Julieta P. Sánchez Arias, Péter Németh, Elisson S. G. de Almeida, Matias A. Ruiz Diaz, Michaela Kraus, Maximiliano Haucke

Abstract: We aim to combine asteroseismology, spectroscopy, and evolutionary models to establish a comprehensive picture of the evolution of Galactic blue supergiant stars (BSG). To start such an investigation, we selected three BSG candidates for our analysis: HD 42087 (PU Gem), HD 52089 ($\epsilon$ CMa) and HD 58350 ($\eta$ CMa). These stars show pulsations and were suspected to be in an evolutionary stage either preceding or succeding the red supergiant (RSG) stage. For our analysis, we utilized the 2-min cadence TESS data to study the photometric variability and obtained new spectroscopic observations at the CASLEO observatory. We calculated CMFGEN non-LTE radiative transfer models and derived stellar and wind parameters using the iterative spectral analysis pipeline XTGRID. The spectral modeling was limited to changing only the effective temperature, surface gravity, CNO abundances, and mass-loss rates. Finally, we compared the derived metal abundances with predictions from Geneva stellar evolution models. The frequency spectra of all three stars show either stochastic oscillations, nonradial strange modes, or a rotational splitting. We conclude that the rather short sectoral observing windows of TESS prevent establishing a reliable mode identification of low frequencies connected to mass-loss variabilities. The spectral analysis confirmed gradual changes in the mass-loss rates and the derived CNO abundances comply with the values reported in the literature. We were able to achieve a quantitative match with stellar evolution models for the stellar masses and luminosities. However, the spectroscopic surface abundances turned out to be inconsistent with theoretical predictions. The stars show N enrichment, typical for CNO cycle processed material, but the abundance ratios do not reflect the associated levels of C and O depletion.

Authors:Jishnu Bhattacharya, Chris S. Hanson, Shravan M. Hanasoge, Katepalli R. Sreenivasan

Abstract: Inertial wave modes in the Sun are of interest owing to their potential to reveal new insight into the solar interior. These predominantly retrograde-propagating modes in the solar subsurface appear to deviate from the thin-shell Rossby-Haurwitz model at high azimuthal orders. We present new measurements of sectoral equatorial inertial modes at $m>15$ where the modes appear to become progressively less retrograde compared to the canonical Rossby-Haurwitz dispersion relation in a co-rotating frame. We use a spectral eigenvalue solver to compute the spectrum of solar inertial modes in the presence of differential rotation. Focussing specifically on equatorial Rossby modes, we find that the numerically obtained mode frequencies lie along distinct ridges, one of which lies strikingly close to the observed mode frequencies in the Sun. We also find that the $n=0$ ridge is deflected strongly in the retrograde direction. This suggests that the solar measurements may not correspond to the fundamental $n=0$ Rossby-Haurwitz solutions as was initially suspected, but to a those for a higher $n$. The numerically obtained eigenfunctions also appear to sit deep within the convection zone -- unlike those for the $n=0$ modes -- which differs substantially from solar measurements and complicates inference.

Authors:B. Snow, M. Druett, A. Hillier

Abstract: Explosive phenomena are known to trigger a wealth of shocks in warm plasma environments, including the solar chromosphere and molecular clouds where the medium consists of both ionised and neutral species. Partial ionisation is critical in determining the behaviour of shocks, since the ions and neutrals locally decouple, allowing for substructure to exist within the shock. Accurately modelling partially ionised shocks requires careful treatment of the ionised and neutral species, and their interactions. Here we study a partially-ionised switch-off slow-mode shock using a multi-level hydrogen model with both collisional and radiative ionisation and recombination rates that are implemented into the two-fluid (P\underline{I}P) code, and study physical parameters that are typical of the solar chromosphere. The multi-level hydrogen model differs significantly from MHD solutions due to the macroscopic thermal energy loss during collisional ionisation. In particular, the plasma temperature both post-shock and within the finite-width is significantly cooler that the post-shock MHD temperature. Furthermore, in the mid to lower chromosphere, shocks feature far greater compression then their single-fluid MHD analogues. The decreased temperature and increased compression reveal the importance of non-equilibrium ionised in the thermal evolution of shocks in partially ionised media. Since partially ionised shocks are not accurately described by the Rankine-Hugoniot shock jump conditions, it may be incorrect to use these to infer properties of lower atmospheric shocks.

Authors:C. A. Nolan, B. Zhao, P. Caselli, Z. Y. Li

Abstract: Radial substructures have now been observed in a wide range of protoplanetary discs (PPDs), from young to old systems, however their formation is still an area of vigorous debate. Recent magnetohydrodynamic (MHD) simulations have shown that rings and gaps can form naturally in PPDs when non-ideal MHD effects are included. However these simulations employ ad-hoc approximations to the magnitudes of the magnetic diffusivities in order to facilitate ring growth. We replace the parametrisation of these terms with a simple chemical network and grain distribution model to calculate the non-ideal effects in a more self-consistent way. We use a range of grain distributions to simulate grain formation for different disc conditions. Including ambipolar diffusion, we find that large grain populations (> 1{\mu}m), and those including a population of very small polyaromatic hydrocarbons (PAHs) facilitate the growth of periodic, stable rings, while intermediate sized grains suppress ring formation. Including Ohmic diffusion removes the positive influence of PAHs, with only large grain populations still producing periodic ring and gap structures. These results relate closely to the degree of coupling between the magnetic field and the neutral disc material, quantified by the non-dimensional Elsasser number {\Lambda} (the ratio of magnetic forces to Coriolis force). For both the ambipolar-only and ambipolar-ohmic cases, if the total Elsasser number is initially of order unity along the disc mid-plane, ring and gap structures may develop.

Authors:Nitin Vashishtha, Satabdwa Majumdar, Ritesh Patel, Vaibhav Pant, Dipankar Banerjee

Abstract: The kinematics of coronal mass ejections (CMEs) are essential for understanding their initiation mechanisms and predicting their planetary impact. Most acceleration and deceleration occur below 4 R$\odot$, which is crucial for initiation understanding. Furthermore, the kinematics of CMEs in the inner corona ($<$ 3 R$_\odot$) are closely related to their propagation in the outer corona and their eventual impact on Earth. Since the CME kinematics are mainly probed using coronagraph data, it is crucial to investigate how imaging cadence affects the precision of data analysis and conclusions drawn and also for determining the flexibility of designing observational campaigns with upcoming coronagraphs. We study ten CMEs observed by the K-Coronagraph of the MLSO. We manually track the CMEs using high cadence (15 s) white-light observations of K-Cor and vary the cadence as 30 s, 1 min, 2 min, and 5 min to study the impact of cadence on the kinematics. We also employed the bootstrapping method to estimate the fitting parameters. Our results indicate that the average velocity of the CMEs does not have a high dependence on the imaging cadence, while the average acceleration shows significant dependence on the same, with the confidence interval showing significant shifts for the average acceleration for different cadences. The decrease in cadence also influences the determination of acceleration onset time. We further find that it is difficult to find an optimum cadence to study all CMEs, as it is also influenced by the pixel resolution of the instrument and the speed of the CME. However, except for very slow CMEs (speeds less than 300 Kms$^{-1}$), our results indicate a cadence of 1 min to be reasonable for the study of their kinematics. The results of this work will be important in the planning of observational campaigns for the existing and upcoming missions that will observe the inner corona.

Authors:Nicholas Storm, Maria Bergemann

Abstract: Yttrium (Y), a key s-process element, is commonly used in nucleosynthesis studies and as a Galactic chemical clock when combined with magnesium (Mg). We study the applicability of the previously assumed LTE line formation assumption in Y abundance studies of main-sequence and red giant stars, and probe the impact of NLTE effects on the [Y/Mg] ratio, a proposed stellar age indicator. We derive stellar parameters, ages, and NLTE abundances of Fe, Mg, and Y for 48 solar analogue stars from high-resolution spectra acquired within the Gaia-ESO survey. For Y, we present a new NLTE atomic model. We determine a solar NLTE abundance of A(Y)$_{\rm NLTE}=2.12\pm0.04$ dex, $0.04$ dex higher than LTE. NLTE effects on Y abundance are modest for optical Y II lines, which are frequently used in Sun-like stars diagnostics. NLTE has a small impact on the [Y/Mg] ratio in such stars. For metal-poor red giants, NLTE effects on Y II lines are substantial, potentially exceeding $+0.5$ dex. For the Gaia/4MOST/WEAVE benchmark star, HD 122563, we find the NLTE abundance ratio of [Y/Fe]$_{\rm NLTE}=-0.55\pm0.04$ dex with consistent abundances obtained from different Y II lines. NLTE has a differential effect on Y abundance diagnostics in late-type stars. They notably affect Y II lines in red giants and very metal-poor stars, which are typical Galactic enrichment tracers of neutron-capture elements. For main-sequence stars, NLTE effects on optical diagnostic Y II lines remain minimal across metallicities. This affirms the [Y/Mg] ratio's reliability as a cosmochronometer for Sun-like stars.

Authors:A. Bensberg, J. Kobus, S. Wolf

Abstract: Context. A characteristic feature of young stellar objects is their variability, which is caused by a variety of different physical processes. High-resolution interferometric observations in the near- and mid-infrared wavelength ranges spanning multiple epochs allow the detailed study of these processes. Aims. We aim at investigating the expected variations of the interferometric observables connected to changes in the measured photometric fluxes of a typical variable accreting central young stellar object with a circumstellar disk. Methods. We calculated visibilities and closure phases as well as the photometric flux of brightness distributions obtained using 3D Monte Carlo radiative transfer simulations for a model of a circumstellar disk with an accreting central star. Results. Changes in the accretion luminosity of the central object, that is, an accreting pre-main-sequence star, can lead to significant variations in the visibility and closure phase of the star-disk system measured with instruments at the Very Large Telescope Interferometer (VLTI) that can be related to changes in the photometric flux. Taking into account additional effects due to baseline variation, interferometric observations can provide valuable contributions to the understanding of the underlying processes. Additionally, we provide the web application VLTI B-VAR that allows the impact of the hour angle on the visibility and closure phase for customized intensity maps to be estimated.

Authors:Can Wang, Feng Chen, Mingde Ding, Zekun Lu

Abstract: We analyse the forces that control the dynamic evolution of a flux rope eruption in a three-dimensional (3D) radiative magnetohydrodynamic (RMHD) simulation. The confined eruption of the flux rope gives rise to a C8.5 flare. The flux rope rises slowly with an almost constant velocity of a few km/s in the early stage, when the gravity and Lorentz force are nearly counterbalanced. After the flux rope rises to the height at which the decay index of the external poloidal field satisfies the torus instability criterion, the significantly enhanced Lorentz force breaks the force balance and drives rapid acceleration of the flux rope. Fast magnetic reconnection is immediately induced within the current sheet under the erupting flux rope, which provides a strong positive feedback to the eruption. The eruption is eventually confined due to the tension force from the strong external toroidal field. Our results suggest that the gravity of plasma plays an important role in sustaining the quasi-static evolution of the pre-eruptive flux rope. The Lorentz force, which is contributed from both the ideal magnetohydrodynamic (MHD) instability and magnetic reconnection, dominates the dynamic evolution during the eruption process.

Authors:Lingfang Wang, Ying Li, Qiao Li, Xin Cheng, Mingde Ding

Abstract: We report on the spectral features of the Si IV 1402.77 \AA, C II 1334.53 \AA, and Mg II h or k lines, formed in the layers from the transition region to the chromosphere, in three two-ribbon flares (with X-, M-, and C-class) observed with IRIS. All the three lines show significant redshifts within the main flare ribbons, which mainly originate from the chromospheric condensation during the flares. The average redshift velocities of the Si IV line within the main ribbons are 56.6, 25.6, and 10.5 km s$^{-1}$ for the X-, M-, and C-class flares, respectively, which show a decreasing tendency with the flare class. The C II and Mg II lines show a similar tendency but with smaller velocities compared to the Si IV line. Additionally, the Mg II h or k line shows a blue-wing enhancement in the three flares in particular at the flare ribbon fronts, which is supposed to be caused by an upflow in the upper chromosphere due to the heating of the atmosphere. Moreover, the Mg II h or k line exhibits a central reversal at the flare ribbons, but turns to pure emission shortly after 1--4 minutes. Correspondingly, the C II line also shows a central reversal but in a smaller region. However, for the Si IV line, the central reversal is only found in the X-class flare, but not in the other two flares. As usual, the central reversal of these lines can be caused by the opacity effect. This implies that in addition to the optically thick lines (C II and Mg II lines), the Si IV line can become optically thick in a strong flare, which is likely related to the nonthermal electron beam heating.

Authors:Yogesh C. Joshi, Alaxendra Panchal

Abstract: We present the results for orbital period analysis of 9 contact binaries (CBs). The photometric data analyzed in this work is collected using ARIES 1-m and 1.3-m telescopes as well as many ground and space-based photometric surveys. The precise orbital periods of the binary systems are studied using the long temporal baseline of data acquired over the last 12-15 years. The changes in the times of minimum brightness are calculated using (O-C) diagram. Out of these 9 CBs, four systems show no change in the orbital period with time while the remaining five systems show non-linear (O-C) variations with time. We derive mass transfer rates for these five CBs which suggests mass is being transferred from secondary to primary components in three systems while it is from primary to secondary components in the other two systems.

Authors:Alaxender Panchal, Yogesh C. Joshi

Abstract: We present the physical parameters of an eclipsing binary system EPIC 211982753 derived through photometric and radial velocity data modeling. We make use of photometric data from NASA's K2 mission, ASAS-SN, and 1.3-m Devasthal Fast Optical Telescope (DFOT) while spectroscopic data have been acquired from the HERMES spectrograph at the 1.2-m Mercator telescope. The linear ephemeris for the system is updated using the K2 mission data. The synthetic light curve and radial velocity curves are generated with the help of eclipsing binary modeling package PHOEBE 1.0. The masses of primary and secondary components are determined as 1.64 $\pm$0.02 and 1.55 $\pm$0.01 $M_{\odot}$, respectively. The radius for primary and secondary components are estimated as 1.73 $\pm$0.02 and 1.47 $\pm$0.02 $R_{\odot}$, respectively. The distance of the system is calculated as 238 $\pm$ 4 pc. The eclipsing binary is found to be a total eclipsing system with a high mass ratio of q=0.94.

Authors:Sierra L. Grant, Lucas M. Stapper, Michiel R. Hogerheijde, Ewine F. van Dishoeck, Sean Brittain, Miguel Vioque

Abstract: The accretion of material from protoplanetary disks onto their central stars is a fundamental process in the evolution of these systems and a key diagnostic in constraining the disk lifetime. We analyze the relationship between the stellar accretion rate and the disk mass in 32 intermediate-mass Herbig Ae/Be systems and compare them to their lower-mass counterparts, T Tauri stars. We find that the $\dot{M}$--$M_{\rm{disk}}$ relationship for Herbig Ae/Be stars is largely flat at $\sim$10$^{-7}$ M$_{\odot}$ yr$^{-1}$ across over three orders of magnitude in dust mass. While most of the sample follows the T Tauri trend, a subset of objects with high accretion rates and low dust masses are identified. These outliers (12 out of 32 sources) have an inferred disk lifetime of less than 0.01 Myr and are dominated by objects with low infrared excess. This outlier sample is likely identified in part by the bias in classifying Herbig Ae/Be stars, which requires evidence of accretion that can only be reliably measured above a rate of $\sim$10$^{-9}$ M$_{\odot}$ yr$^{-1}$ for these spectral types. If the disk masses are not underestimated and the accretion rates are not overestimated, this implies that these disks may be on the verge of dispersal, which may be due to efficient radial drift of material or outer disk depletion by photoevaporation and/or truncation by companions. This outlier sample likely represents a small subset of the larger young, intermediate-mass stellar population, the majority of which would have already stopped accreting and cleared their disks.

Authors:Yulei Wang, Xin Cheng, Mingde Ding, Zhaoyuan Liu, Jian Liu, Xiaojue Zhu

Abstract: Solar flares can release coronal magnetic energy explosively and may impact the safety of near-earth space environments. Their structures and properties on macroscale have been interpreted successfully by the generally-accepted two-dimension standard model invoking magnetic reconnection theory as the key energy conversion mechanism. Nevertheless, some momentous dynamical features as discovered by recent high-resolution observations remain elusive. Here, we report a self-consistent high-resolution three-dimension magnetohydrodynamical simulation of turbulent magnetic reconnection within a flare current sheet. It is found that fragmented current patches of different scales are spontaneously generated with a well-developed turbulence spectrum at the current sheet, as well as at the flare loop-top region. The close coupling of tearing-mode and Kelvin-Helmholtz instabilities plays a critical role in developing turbulent reconnection and in forming dynamical structures with synthetic observables in good agreement with realistic observations. The sophisticated modeling makes a paradigm shift from the traditional to three-dimension turbulent reconnection model unifying flare dynamical structures of different scales.

Authors:Deepak Chahal, Devika Kamath, Richard de Grijs, Paolo Ventura, Xiaodian Chen

Abstract: In our recent catalogue of BY Draconis (BY Dra) variables based on Zwicky Transient Facility data, we found traces of a period gap in the period-colour diagram. We combined our BY Dra database with catalogues from the {\sl Kepler} and K2 surveys, revealing a prominent period gap. Here, we use this combined ZTF-{\sl Kepler}-K2 data set to investigate the origin of the period gap observed for BY Dra stars using chromospheric activity indices. We use low- and medium-resolution spectra from the LAMOST Data Release 7 to derive magnetic activity indices for the Ca {\sc ii} H and K and H$\alpha$ emission lines. We find a strong dependence of chromospheric activity on both stellar mass and rotation period. For partially convective K-M-type stars, the activity decreases steeply up to an age of $\sim$700-1000 Myr, subsequently evolving to the type of low-level saturation associated with spin-down stallation. In contrast, F-G-type stars with thinner convective envelopes exhibit constant activity with increasing age. We suspect that the observed steep decrease for partially convective stars is driven by core-envelope coupling. This mechanism reduces differential rotation at the core-envelope transition, hence leading to decreased magnetic activity. Moreover, we derive activity indices for previously known star clusters and find similar trends as regards their activity levels as a function of age. In particular, very low-level activity is observed around the location of the period gap. Therefore, we conclude that the period gap, defined by the non-detection of variable sources, is driven by a minimum in chromospheric activity.

Authors:Sihui Zhong, Valery M. Nakariakov, Dmitrii Y. Kolotkov, Lakshmi Pradeep Chitta, Patrick Antolin, Cis Verbeeck, David Berghmans

Abstract: Decayless kink oscillations of plasma loops in the solar corona may contain an answer to the enigmatic problem of solar and stellar coronal heating. The polarisation of the oscillations gives us a unique information about their excitation mechanisms and energy supply. However, unambiguous determination of the polarisation has remained elusive. Here, we show simultaneous detection of a 4-min decayless kink oscillation from two non-parallel lines-of-sights, separated by about 104\textdegree, provided by unique combination of the High Resolution Imager on Solar Orbiter and the Atmospheric Imaging Assembly on Solar Dynamics Observatory. The observations reveal a horizontal or weakly oblique linear polarisation of the oscillation. This conclusion is based on the comparison of observational results with forward modelling of the observational manifestation of various kinds of polarisation of kink oscillations. The revealed polarisation favours the sustainability of these oscillations by quasi-steady flows which may hence supply the energy for coronal heating.

Authors:D. Nardiello, L. R. Bedin, M. Griggio, M. Salaris, M. Scalco, S. Cassisi

Abstract: In the third paper of this series aimed at developing the tools for analysing resolved stellar populations using the cameras on board of the James Webb Space Telescope (JWST), we present a detailed multi-band study of the 2 Gyr Galactic open cluster NGC 2506. We employ public calibration data-sets collected in multiple filters to: (i) derive improved effective Point Spread Functions (ePSFs) for ten NIRCam filters; (ii) extract high-precision photometry and astrometry for stars in the cluster, approaching the main-sequence (MS) lower mass of ~0.1 Msun; and (iii) take advantage of the synergy between JWST and Gaia DR3 to perform a comprehensive analysis of the cluster's global and local properties. We derived a MS binary fraction of ~57.5 %, extending the Gaia limit (~0.8 Msun) to lower masses (~0.4 Msun) with JWST. We conducted a study on the mass functions (MFs) of NGC 2506, mapping the mass segregation with Gaia data, and extending MFs to lower masses with the JWST field. We also combined information on the derived MFs to infer an estimate of the cluster present-day total mass. Lastly, we investigated the presence of white dwarfs (WDs) and identified a strong candidate. However, to firmly establish its cluster membership, as well as that of four other WD candidates and of the majority of faint low-mass MS stars, further JWST equally deep observations will be required. We make publicly available catalogues, atlases, and the improved ePSFs.

Authors:Jerry Jun-Yan Zhang, Nicolas Lodieu, Eduardo Martín

Abstract: Context. Metal-poor brown dwarfs are poorly understood because they are extremely faint and rare. Only a few candidates have been identified as T-type subdwarfs in infrared surveys and their optical properties remain unconstrained. Aims. We aim to improve the knowledge of the optical properties of T subdwarf candidates to break the degeneracy between metallicity and temperature and to investigate their atmospheric properties. Methods. Deep $z$-band images of 10 known T subdwarf candidates were collected with the 10.4-m Gran Telescopio Canarias. Low-resolution optical spectra for two of them were obtained with the same telescope. Photometric measurements of the $z$-band flux were performed for all the targets and they were combined with infrared photometry in $J, H, K, W1$ and $W2$-bands from the literature to obtain the colours. The spectra were compared with solar-metallicity T dwarf templates and with laboratory spectra. Results. We found that the targets segregate into three distinct groups in the $W1 - W2$ vs. $z - W1$ colour-colour diagram. Group I objects are mixed with solar-metallicity T dwarfs. Group III objects have $W1 - W2$ colours similar to T dwarfs but very red $z - W1$ colours. Group II objects lie between Group I and III. The two targets for which we obtained spectra are located in Group I and their spectroscopic properties resemble normal T dwarfs but with water features that are deeper and have a shape akin to pure water. Conclusions. We conclude that the $W1 - W2$ vs. $z - W1$ colour-colour diagram is excellent to break the metallicity-temperature degeneracy for objects cooler than L-type. A revision of the spectral classification of T subdwarf might be needed in the future, according to the photometric and spectroscopic properties of WISE1810 and WISE0414 in Group III discussed in this work.

Authors:Chengyuan Wu, Heran Xiong, Zhanwen Han, Bo Wang

Abstract: Double white dwarf (WD) merger process and their post-merger evolution are important in many fields of astronomy, such as supernovae, gamma-ray bursts, gravitational waves, etc. The evolutionary outcomes of double ultra-massive WD merger remnants are still a subject of debate, though the general consensus is that the merger remnant will collapse to form a neutron star. In this work, we investigate the evolution of a 2.20Msun merger remnant stemmed from the coalescence of double 1.10Msun ONe WDs. We find that the remnant ignites off-centre neon burning at the position near the surface of primary WD soon after the merger, resulting in the stable inwardly propagating oxygen/neon (O/Ne) flame. The final outcomes of the merger remnant are sensitive to the effect of convective boundary mixing. If the mixing cannot stall the O/Ne flame, the flame will reach the centre within 20 years, leading to the formation of super Chandrasekhar mass silicon core, and its final fate probably be neutron star (NS) through iron-core-collapse supernova. In contrast, if the convective mixing is effective enough to prevent the O/Ne flame from reaching the centre, the merger remnant will undergo electron capture supernova to form an ONeFe WD. Meanwhile, we find that the wind mass loss process may hardly alter the final fate of the remnant due to its fast evolution. Our results imply that the coalescence of double ONe WDs can form short lived giant like object, but the final outcomes (NS or ONeFe WD) are influenced by the uncertain convective mixing in O/Ne flame.

Authors:Tomek Kaminski, Mirek R. Schmidt, Anlaug Amanda Djupvik, Karl M. Menten, Alex Kraus, Krystian Iłkiewicz, Thomas Steinmetz, Muhammad Zain Mobeen, Ryszard Szczerba

Abstract: U Equ is an unusual maser-hosting IR source discovered in the 1990s. It was tentatively classified as a post-AGB star with a unique optical spectrum displaying rare emission and absorption features from molecular gas. In 2022, we discovered that its optical spectrum has drastically changed. Methods: Optical high-resolution spectra of U Equ from SALT are supplemented by archival data and NIR photometry from NOT. New spectral line observations with the Effelsberg telescope and ALMA are presented. Results: No circumstellar molecular features are present in the contemporary optical spectra of U Equ. Non-photospheric absorption and emission from neutral and ionized species dominate the current spectrum. Some of the observed features indicate an outflow with a terminal velocity of 215 km\s. The H\&K lines of [Ca II] indicate a photosphere of spectral type F. Photometric measurements show that the source has been monotonically increasing its optical and NIR fluxes since the beginning of this century. SEDs at different epochs show dusty circumstellar material arranged in a highly-inclined disk. At a distance of 4 kpc, the source's luminosity is 10$^4$ L$_{\odot}$. Conclusions: The object has changed considerably in the last three decades, either due to geometrical reconfiguration of the circumstellar medium, evolutionary changes in the central star, or owing to an accretion event that has started in the system very recently. Observationally, U Equ appears to resemble the Category 0 of disk-hosting post-AGB stars, especially the post-common envelope binary HD 101584. It is uncertain if the drastic spectral change and the associated optical/MIR rise in brightness are common in post-AGB stars but such a radical change may be related to the real-time onset of the evolution of the system into a planetary nebula. We find that the post-AGB star V576 Car has undergone a similar transformation as U Equ.

Authors:Simon Blouin, Falk Herwig, Huaqing Mao, Pavel Denissenkov, Paul R. Woodward

Abstract: The inner structure of core-helium burning (CHeB) stars remains uncertain due to the yet unknown nature of mixing at the boundary of their cores. Large convective cores beyond a bare Schwarzschild model are favoured both from theoretical arguments and from asteroseismological constraints. However, the exact nature of this extra mixing, and in particular the possible presence of semiconvective layers, is still debated. In this work, we approach this problem through a new avenue by performing the first full-sphere 3D hydrodynamics simulations of the interiors of CHeB stars. We use the PPMstar explicit gas dynamics code to simulate the inner 0.45 $M_{\odot}$ of a 3 $M_{\odot}$ CHeB star. Simulations are performed using different Cartesian grid resolutions (768$^3$, 1152$^3$ and 1728$^3$) and heating rates. We use two different initial states, one based on MESA's predictive mixing scheme (which yields a large overshoot region) and one based on the convective premixing approach (which exhibits a semiconvective interface). The general behaviour of the flow in the convective core and in the stable envelope (where internal gravity waves are observed) is consistent with our recent simulations of core convection in massive main-sequence stars, and so are the various scaling relations. The semiconvective layers are dominated by strong internal gravity waves that do not produce measurable species mixing, but overshooting motions from the convective core gradually homogenize the semiconvective interface. This process can possibly completely erase the semiconvective layers, which would imply that CHeB stars do not harbour a semiconvection zone.

Authors:S. Hubrig, S. P. Jarvinen, J. D. Alvarado-Gomez, I. Ilyin, M. Schöller

Abstract: Numerous delta Sct and gamma Dor pulsators are identified in the region of the Hertzsprung-Russell diagram that is occupied by chemically peculiar magnetic Ap stars. The connection between delta Sct and gamma Dor pulsations and the magnetic field in Ap stars is however not clear: theory suggests for magnetic Ap stars some critical field strengths for pulsation mode suppression by computing the magnetic damping effect for selected p and g modes. To test these theoretical considerations, we obtained PEPSI spectropolarimetric snapshots of the typical Ap star HD340577, for which delta Sct-like pulsations were recently detected in TESS data, and the gamma Dor pulsator HR8799, which is a remarkable system with multiple planets and two debris disks. Our measurements reveal the presence of a magnetic field with a strength of several hundred Gauss in HD340577. The measured mean longitudinal field would be the strongest field measured so far in a delta Sct star if the pulsational character of HD340577 is confirmed spectroscopically. No magnetic field is detected in HR8799.

Authors:Jing Ye, John C. Raymond, Zhixing Mei, Qiangwei Cai, Yuhao Chen, Yan Li, Jun Lin

Abstract: Turbulence plays a key role for forming the complex geometry of the large-scale current sheet (CS) and fast energy release in a solar eruption. In this paper, we present full 3D high-resolution simulations for the process of a moderate Coronal Mass Ejection (CME) and the thermodynamical evolution of the highly confined CS. Copious elongated blobs are generated due to tearing and plasmoid instabilities giving rise to a higher reconnection rate and undergo the splitting, merging and kinking processes in a more complex way in 3D. A detailed thermodynamical analysis shows that the CS is mainly heated by adiabatic and numerical viscous terms, and thermal conduction is the dominant factor that balances the energy inside the CS. Accordingly, the temperature of the CS reaches to a maximum of about 20 MK and the range of temperatures is relatively narrow. From the face-on view in the synthetic Atmospheric Imaging Assembly 131 $\mathring{A}$, the downflowing structures with similar morphology to supra-arcade downflows are mainly located between the post-flare loops and loop-top, while moving blobs can extend spikes higher above the loop-top. The downward-moving plasmoids can keep the twisted magnetic field configuration until the annihilation at the flare loop-top, indicating that plasmoid reconnection dominates in the lower CS. Meanwhile, the upward-moving ones turn into turbulent structures before arriving at the bottom of the CME, implying that turbulent reconnection dominates in the upper CS. The spatial distributions of the turbulent energy and anisotropy are addressed, which show a significant variation in the spectra with height.

Authors:Justyn Campbell-White, Carlo F. Manara, Myriam Benisty, Antonella Natta, Rik A. B. Claes, Antonio Frasca, Jaehan Bae, Stefano Facchini, Andrea Isella, Laura Pérez, Paola Pinilla, Aurora Sicilia-Aguilar, Richard Teague

Abstract: PDS 70 is so far the only young disc where multiple planets have been detected by direct imaging. The disc has a large cavity when seen at sub-mm and NIR wavelengths, which hosts two massive planets. This makes PDS 70 the ideal target to study the physical conditions in a strongly depleted inner disc shaped by two giant planets, and in particular to test whether disc winds can play a significant role in its evolution. Using X-Shooter and HARPS spectra, we detected for the first time the wind-tracing [O I] 6300AA line, and confirm the low-moderate value of mass-accretion rate in the literature. The [O I] line luminosity is high with respect to the accretion luminosity when compared to a large sample of discs with cavities in nearby star-forming regions. The FWHM and blue-shifted peak of the [O I] line suggest an emission in a region very close to the star, favouring a magnetically driven wind as the origin. We also detect wind emission and high variability in the He I 10830AA line, which is unusual for low-accretors. We discuss that, although the cavity of PDS 70 was clearly carved out by the giant planets, the substantial inner disc wind could also have had a significant contribution to clearing the inner-disc.

Authors:I. G. Richardson NASA Goddard Space Flight Center and University of Maryland, College Park, O. C. St Cyr NCAR/HAO, J. T. Burkepile NCAR/HAO, H. Xie NASA Goddard Space Flight Center and Catholic University of America, B. J. Thompson NASA Goddard Space Flight Center

Abstract: We report on the first comprehensive study of the coronal mass ejections (CMEs) associated with $\sim$25 MeV solar energetic proton (SEP) events in 1980-2013 observed in the low/inner corona by the Mauna Loa Solar Observatory (MLSO) Mk3 and Mk4 coronameters. Where possible, these observations are combined with spacebased observations from the Solar Maximum Mission C/P, P78-1 SOLWIND or SOHO/LASCO coronagraphs. The aim of the study is to understand directly-measured (rather than inferred from proxies) CME motions in the low to middle corona and their association with SEP acceleration, and hence attempt to identify early signatures that are characteristic of SEP acceleration in ground-based CME observations that may be used to warn of impending SEP events. Although we find that SEP events are associated with CMEs that are on average faster and wider than typical CMEs observed by MLSO, a major challenge turns out to be determining reliable estimates of the CME dynamics in the low corona from the 3-minute cadence Mk3/4 observations since different analysis techniques can produce inconsistent results. This complicates the assessment of what early information on a possible SEP event is available from these low coronal observations

Authors:V. P. Grinin, L. V. Tambovtseva, A. A. Djupvik, G. Gahm, T. Grenman, H. Weber, H. Bengtsson, H. De Angelis, G. Duszanowicz, D. Heinonen, G. Holmberg, T. Karlsson, M. Larsson, J. Warell, T. Wikander

Abstract: Based on observations obtained with the Nordic Optical Telescope we investigate the spectral variability of the Herbig Ae star RR Tau. This star belongs to the UX Ori family, characterized by very deep fadings caused by the screening of the star with opaque fragments (clouds) of the protoplanetary discs. At the moments of such minima one observes strong spectral variability due to the fact that the dust cloud occults, for an observer, not only the star but also a part of the region where the emission spectrum originates. We calculated a series of obscuration models to interpret the observed variability of the H-alpha line parameters. We consider two main obscuration scenarios: (1) the dust screen rises vertically above the circumstellar disc, and (2) the screen intersects the line-of-sight moving azimuthally with the disc. In both cases the model of the emission region consists of a compact magnetosphere and a magneto-centrifugal disc wind. Comparison with observations shows that the first scenario explains well the variability of the radiation flux, the equivalent width, as well as the asymmetry of the H-alpha line during eclipses, while the second scenario explains them only partly. This permits us to suggest that in the case of RR Tau, the main causes of the eclipses are either a structured disc wind, or the charged dust lifted along the field lines of the poloidal component of the magnetic field of the circumstellar disc.

Authors:Travis S. Metcalfe, Derek Buzasi, Daniel Huber, Marc H. Pinsonneault, Jennifer L. van Saders, Thomas R. Ayres, Sarbani Basu, Jeremy J. Drake, Ricky Egeland, Oleg Kochukhov, Pascal Petit, Steven H. Saar, Victor See, Keivan G. Stassun, Yaguang Li, Timothy R. Bedding, Sylvain N. Breton, Adam J. Finley, Rafael A. Garcia, Hans Kjeldsen, Martin B. Nielsen, J. M. Joel Ong, Jakob L. Rorsted, Amalie Stokholm, Mark L. Winther, Catherine A. Clark, Diego Godoy-Rivera, Ilya V. Ilyin, Klaus G. Strassmeier, Sandra V. Jeffers, Stephen C. Marsden, Aline A. Vidotto, Sallie Baliunas, Willie Soon

Abstract: The bright star $\lambda$ Ser hosts a hot Neptune with a minimum mass of 13.6 $M_\oplus$ and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system, and to constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite (TESS), and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and to estimate the wind braking torque. We conclude that the remaining uncertainty on stellar age currently prevents an unambiguous interpretation of the properties of $\lambda$ Ser, and that the rate of angular momentum loss appears to be higher than for other stars with similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.

Authors:Galina Chikunova, Tatiana Podladchikova, Karin Dissauer, Astrid M. Veronig, Mateja Dumbović, Manuela Temmer, Ewan C. M. Dickson

Abstract: We investigate the relation between the spatiotemporal evolution of the dimming region and the dominant direction of the filament eruption and CME propagation for the 28 October 2021 X1.0 flare/CME event observed from multiple viewpoints by Solar Orbiter, STEREO-A, SDO, and SOHO. We propose a method to estimate the dominant dimming direction by tracking its area evolution and emphasize its accurate estimation by calculating the surface area of a sphere for each pixel. To determine the early flux rope propagation direction, we perform 3D reconstruction of the CME via graduated cylindrical shell modeling (GCS) and tie-pointing of the filament. The dimming initially expands radially and later shifts southeast. The orthogonal projections of the reconstructed height evolution of the erupting filament onto the solar surface are located in the sector of the dominant dimming growth, while the orthogonal projections of the inner part of GCS reconstruction align with the total dimming area. The filament reaches a maximum speed of $\approx$250 km/s at a height of about $\approx$180 Mm. The direction of its motion is strongly inclined from the radial (64$^\circ$ to the East, 32$^\circ$ to the South). The 50$^\circ$ difference in the 3D direction between the CME and the filament leg closely corresponds to the CME half-width determined from reconstruction, suggesting a potential relation of the reconstructed filament to the associated leg of the CME body. Our findings highlight that the dominant propagation of the dimming growth reflects the direction of the erupting magnetic structure (filament) low in the solar atmosphere, though the filament evolution is not related directly to the direction of the global CME expansion. The overall dimming morphology closely resembles the inner part of the CME reconstruction, validating the use of dimming observations to obtain insight into the CME direction.

Authors:Matthew Shelby, Scott Scharlach, Petar Matejic, RJ Everett, Colton Morgan

Abstract: Although a variety of phenomena may create a geomagnetic storm on Earth, the most severe geomagnetic storms arise from solar activity, and in particular, coronal mass ejections (CMEs) and solar flares. CMEs and flares originate primarily from sunspots. The "aa index" is a metric which ranks all of the strongest geomagnetic storms between 1868 and 2010 based on a variety of characteristics taken from several sources. This paper examines correlations between the aa index of the most severe geomagnetic storms and the intrinsic characteristics of the sunspots from which they originated. We find a correlation between the total rank of the aa index of the storms and the "total intensity" of the sunspot, where total intensity is defined as the sunspot's mean intensity multiplied by its area. The correlation has an R-Squared = 0.690 and R-Squared = 0.855 when a potentially corrupted data point is removed.

Authors:Joel C. Zinn, Marc H. Pinsonneault, Lars Bildsten, Dennis Stello

Abstract: Although stellar radii from asteroseismic scaling relations agree at the percent level with independent estimates for main sequence and most first-ascent red giant branch stars, the scaling relations over-predict radii at the tens of percent level for the most luminous stars ($R \gtrsim 30 R_{\odot}$). These evolved stars have significantly superadiabatic envelopes, and the extent of these regions increase with increasing radius. However, adiabaticity is assumed in the theoretical derivation of the scaling relations as well as in corrections to the large frequency separation. Here, we show that a part of the scaling relation radius inflation may arise from this assumption of adiabaticity. With a new reduction of Kepler asteroseismic data, we find that scaling relation radii and Gaia radii agree to within at least $2\%$ for stars with $R \lesssim 30 R_{\odot}$, when treated under the adiabatic assumption. The accuracy of scaling relation radii for stars with $50 R_{\odot} \lesssim R \lesssim 100 R_{\odot}$, however, is not better than $10\%-15\%$ using adiabatic large frequency separation corrections. We find that up to one third of this disagreement for stars with $R \approx 100 R_{\odot}$ could be caused by the adiabatic assumption, and that this adiabatic error increases with radius to reach $10\%$ at the tip of the red giant branch. We demonstrate that, unlike the solar case, the superadiabatic gradient remains large very deep in luminous stars. A large fraction of the acoustic cavity is also in the optically thin atmosphere. The observed discrepancies may therefore reflect the simplified treatment of convection and atmospheres.

Authors:Jinhan Guo, Ye Qiu, Yiwei Ni, Yang Guo, Chuan Li, Yuhang Gao, Brigitte Schmieder, Stefaan Poedts, Pengfei Chen

Abstract: Solar filaments often exhibit rotation and deflection during eruptions, which would significantly affect the geoeffectiveness of the corresponding coronal mass ejections (CMEs). Therefore, understanding the mechanisms that lead to such rotation and lateral displacement of filaments is a great concern to space weather forecasting. In this paper, we examine an intriguing filament eruption event observed by the Chinese H{\alpha} Solar Explorer (CHASE) and the Solar Dynamics Observatory (SDO). The filament, which eventually evolves into a CME, exhibits significant lateral drifting during its rising. Moreover, the orientation of the CME flux rope axis deviates from that of the pre-eruptive filament observed in the source region. To investigate the physical processes behind these observations, we perform a data-constrained magnetohydrodynamic (MHD) simulation. Many prominent observational features in the eruption are reproduced by our numerical model, including the morphology of the eruptive filament, eruption path, and flare ribbons. The simulation results reveal that the magnetic reconnection between the flux-rope leg and neighboring low-lying sheared arcades may be the primary mechanism responsible for the lateral drifting of the filament material. Such a reconnection geometry leads to flux-rope footpoint migration and a reconfiguration of its morphology. As a consequence, the filament material hosted in the flux rope drifts laterally, and the CME flux rope deviates from the pre-eruptive filament. This finding underscores the importance of external magnetic reconnection in influencing the orientation of a flux rope axis during eruption.

Authors:P. P. Petrov, K. N. Grankin, E. V. Babina, S. A. Artemenko, M. M. Romanova, S. Yu. Gorda, A. A. Djupvik, J. F. Gameiro

Abstract: Spectral and photometric variability of the Classical T Tauri stars RY Tau and SU Aur from 2013 to 2022 is analyzed. We find that in SU Aur the H-alpha line's flux at radial velocity RV = -50 +- 7 km/s varies with a period P = 255 +- 5 days. A similar effect previously discovered in RY Tau is confirmed with these new data: P = 21.6 days at RV = -95 +- 5 km/s. In both stars, the radial velocity of these variations, the period, and the mass of the star turn out to be related by Kepler's law, suggesting structural features on the disc plane orbiting at radii of 0.2 AU in RY Tau and 0.9 AU in SU Aur, respectively. Both stars have a large inclination of the accretion disc to the line of sight - so that the line of sight passes through the region of the disc wind. We propose there is an azimuthal asymmetry in the disc wind, presumably in the form of 'density streams', caused by substructures of the accretion disc surface. These streams cannot dissipate until they go beyond the Alfven surface in the disc's magnetic field. These findings open up the possibility to learn about the structure of the inner accretion disc of CTTS on scales less than 1 AU and to reveal the orbital distances related to the planet's formation.

Authors:Somayeh Soomandar, Atila Poro

Abstract: This study presented a new analysis for the TESS-observed W Ursae Majoris (W UMa) binary star YY Coronea Borealis (YY CrB). The light curve was analyzed by the PHysics Of Eclipsing BinariEs (PHOEBE) Python version together with the Markov chain Monte Carlo (MCMC) method. The light curve solutions required a hot spot and l3. New eclipse times from the TESS observations were extracted, and the O-C curve of primary and secondary minima showed an anti-correlated manner. In order to study the O-C curve of minima, minima times between 1991 and 2023 were collected. This investigation reported a new linear ephemeris and by fitting a quadratic function to the O-C curve of minima, calculated the orbital period rate of \mathop P\limits^.\approx 5.786*{10^{-8}} day/year. Assuming mass conservation, a mass exchange rate of \mathop{{M_2}}\limits^.=2.472*{10^{-8}} calculated from the more massive component to the less massive one. Then, by using the light travel time function, the possible third body was determined in the binary and derived the mass of the third body as 0.498M_Sun with a period of \simeq 7351.018 days. The O-C curve analysis and the quantity of mass indicate that the presence of a third body is unlikely. This binary is expected to evolve into a broken-contact phase and is a good case to support the thermal relaxation oscillation model.

Authors:I. Piantschitsch, J. Terradas, E. Soubrie, S. G. Heinemann, S. J. Hofmeister, R. Soler, M. Temmer

Abstract: Interactions between global coronal waves (CWs) and coronal holes (CHs) reveal many interesting features of reflected waves and coronal hole boundaries (CHB) but have fairly been studied so far. Magnetohydrodynamic (MHD) simulations can help us to better understand what is happening during these interaction events, and therefore, to achieve a broader understanding of the parameters involved. In this study, we perform for the first time 2D MHD simulations of a CW-CH interaction including a realistic initial wave density profile that consists of an enhanced as well as a depleted wave part. We vary several initial parameters, such as the initial density amplitudes of the incoming wave, the CH density, and the CHB width, which are all based on actual measurements. We analyse the effects of different incident angles on the interaction features and we use the corresponding time-distance plots to detect specific features of the incoming and the reflected wave. We found that a particular combination of a small CH density, a realistic initial density profile and a sufficiently small incident angle leads to remarkable interaction features, such as a large density amplitude of the reflected wave with respect to the incoming one. The parameter studies in this paper provide a tool to compare time-distance plots based on observational measurements to those created from simulations and therefore enable us to derive interaction parameters from observed CW-CH interaction events that usually cannot be obtained directly. The simulation results in this study are augmented by analytical expressions for the reflection coefficient of the CW-CH interaction which allows us to verify the simulations results in an additional way. This work is the first of a series of studies aiming to finally reconstruct actual observed CW-CH interaction events by means of MHD-simulations.

Authors:Johanna Jurcsik, Gergely Hajdu

Abstract: Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The $G$-band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new ${\mathrm{[Fe/H]}}_{\mathrm{phot}}- P,\varphi_{31}$ formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multi-parameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published ${\mathrm{[Fe/H]}}_{\mathrm{phot}}$ values and the results of the available photometric formulae in the Gaia $G$-band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain.

Authors:N. Kleeorin, I. Rogachevskii, N. Safiullin, R. Gershberg, S. Porshnev

Abstract: Our theoretical and numerical analysis have suggested that for low-mass main sequences stars (of the spectral classes from M5 to G0) rotating much faster than the sun, the generated large-scale magnetic field is caused by the mean-field $\alpha^2\Omega$ dynamo, whereby the $\alpha^2$ dynamo is modified by a weak differential rotation. Even for a weak differential rotation, the behaviour of the magnetic activity is changed drastically from aperiodic regime to nonlinear oscillations and appearance of a chaotic behaviour with increase of the differential rotation. Periods of the magnetic cycles decrease with increase of the differential rotation, and they vary from tens to thousand years. This long-term behaviour of the magnetic cycles may be related to the characteristic time of the evolution of the magnetic helicity density of the small-scale field. The performed analysis is based on the mean-field numerical simulations of the $\alpha^2\Omega$ and $\alpha^2$ dynamos and a developed nonlinear theory of $\alpha^2$ dynamo.

Authors:Daniel Tafoya, Peter A. M. van Hoof, Jesus A. Toala, Griet Van de Steene, Suzanna Randall, Ramlal Unnikrishnan, Stefan Kimeswenger, Marcin Hajduk, Daniela Barria, Albert Zijlstra

Abstract: We present high angular-resolution observations of Sakurai's object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission, observed at an angular resolution of 20 milliarcsec (corresponding to 70 AU), reveals a bright compact central component whose spectral index indicates that it composed of amorphous carbon dust. Based on these findings, we conclude that this emission traces the previously suggested dust disc observed in mid-infrared observations. Therefore, our observations provide the first direct imaging of such a disc. The H$^{12}$CN($J$=4$\rightarrow$3) line emission, observed at an angular resolution of 300 milliarcsec (corresponding to 1000 AU), displays bipolar structure with a north-south velocity gradient. From the position-velocity diagram of this emission we identify the presence of an expanding disc and a bipolar molecular outflow. The inclination of the disc is determined to be $i$=72$^\circ$. The derived values for the de-projected expansion velocity and the radius of the disc are $v_{\rm exp}$=53 km s$^{-1}$ and $R$=277 AU, respectively. On the other hand, the de-projected expansion velocity of the bipolar outflow detected in the H$^{12}$CN($J$=4$\rightarrow$3) emission of approximately 1000 km s$^{-1}$. We propose that the molecular outflow has an hourglass morphology with an opening angle of around 60$^{\circ}$. Our observations unambiguously show that an equatorial disc and bipolar outflows formed in Sakurai's object in less than 30 years after the born-again event occurred, providing important constraints for future modelling efforts of this phenomenon.

Authors:R. Wesson, Mikako Matsuura, Albert A. Zijlstra, Kevin Volk, Patrick J. Kavanagh, Guillermo García-Segura, I. McDonald, Raghvendra Sahai, M. J. Barlow, Nick L. J. Cox, Jeronimo Bernard-Salas, Isabel Aleman, Jan Cami, Nicholas Clark, Harriet L. Dinerstein, K. Justtanont, Kyle F. Kaplan, A. Manchado, Els Peeters, Griet C. Van de Steene, Peter A. M. van Hoof

Abstract: We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6$\mu$m to 25 $\mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H$_2$, with a characteristic diameter of 0.2 arcsec and density $n_{\rm H} \sim 10^5$-$10^6$ cm$^{-3}$. The shell contains a thin ring of polycyclic aromatic hydrocarbon (PAH) emission. H$_2$ is found throughout the shell and in the halo. H$_2$ in the halo may be located on the swept-up walls of a biconal polar flow. The central cavity is shown to be filled with high ionization gas and shows two linear structures. The central star is located 2 arcsec from the emission centroid of the cavity and shell. Linear features (`spikes') extend outward from the ring, pointing away from the central star. Hydrodynamical simulations are shown which reproduce the clumping and possibly the spikes. Around ten low-contrast, regularly spaced concentric arc-like features are present; they suggest orbital modulation by a low-mass companion with a period of about 280 yr. A previously known much wider companion is located at a projected separation of about 15 000 au; we show that it is an M2-M4 dwarf. The system is therefore a triple star. These features, including the multiplicity, are similar to those seen in the Southern Ring Nebula (NGC 3132) and may be a common aspect of such nebulae.

Authors:R. Wesson, A. M. Bevan, M. J. Barlow, I. De Looze, M. Matsuura, G. Clayton, J. Andrews

Abstract: We present a study of the dust associated with the core-collapse supernova SN~1995N. Infrared emission detected 14--15 years after the explosion was previously attributed to thermally echoing circumstellar material associated with the SN progenitor. We argue that this late-time emission is unlikely to be an echo, and is more plausibly explained by newly formed dust in the supernova ejecta, indirectly heated by the interaction between the ejecta and the CSM. Further evidence in support of this scenario comes from emission line profiles in spectra obtained 22 years after the explosion; these are asymmetric, showing greater attenuation on the red wing, consistent with absorption by dust within the expanding ejecta. The spectral energy distribution and emission line profiles at epochs later than $\sim$5000 days are both consistent with the presence of about 0.4~M$_\odot$ of amorphous carbon dust. The onset of dust formation is apparent in archival optical spectra, taken between 700 and 1700 days after the assumed explosion date. As this is considerably later than most other instances where the onset of dust formation has been detected, we argue that the explosion date must be later than previously assumed.

Authors:Félix Llorente de Andrés

Abstract: A recent study shows, from an empirical deduction, that the number and the presence of the blue straggler stars (BSS) in an open cluster follow a function whose components are the ratio between age and the relaxation time, $\it f$, and a factor, $\varpi$ , which is an indicator of stellar collisions plus primordial binaries. The relation among the number of blue straggler stars, the factor $\it f$, and the factor $\varpi$ of each globular cluster allows for deriving the age of the respective globular clusters. This method has been applied individually over 56 globular clusters containing BSS. The values derived for the cluster ages from our methodology do not differ from those derived from other methods. A special case is cluster NGC 104 whose age exceeds 13.8 Gyr (its age is between 19.04 and 20.30 Gyr), which would have a very exotic explanation: the existence of an intermediate black hole in the center of the cluster. That black hole main-sequence star (BH-MS) binaries with an initial orbital period less than the bifurcation period can evolve into ultra-compact X-ray binaries (UCXBs) that can be detected by LISA. On the other hand, if that age were true, it would call into question the expansion velocity for a flat Universe. This would call into question the case for dark energy dominated Universe.

Authors:C. J. Schrijver

Abstract: This invited memoir looks back on my scientific career that straddles the solar and stellar branches of astrophysics, with sprinklings of historical context and personal opinion. Except for a description of my life up to my Ph.D. phase, the structure is thematic rather than purely chronological, focusing on those topics that I worked on throughout substantial parts of my life: stars like the Sun and the Sun-as-a-star, surface field evolution, coronal structure and dynamics, heliophysics education, and space weather. Luck and a broadly inquisitive frame of mind shaped a fortunate life on two continents, taking me from one amazing mentor, colleague, and friend to another, working in stimulating settings to interpret data from state-of-the-art space observatories.

Authors:Sadhana Singh, Jeewan C. Pandey, Vishal Joshi

Abstract: Using the linear polarimetric observations, we present a method to derive the membership probability of stars in cluster NGC 2345. The polarimetric observations of cluster NGC 2345 are performed using the instrument ARIES IMaging POLarimeter (AIMPOL) mounted as a backend of the 104-cm telescope of ARIES. Members of the cluster should exhibit comparable polarization since they are located nearly at the same distance. This concept is used to extract the membership probability of known member stars of cluster NGC 2345. The membership probability estimated using the polarimetric data for cluster NGC 2345 agrees with the membership probability derived from the proper motion method in the previous studies.

Authors:Philippa Browning, Mykola Gordovskyy, Alan Hood

Abstract: Twisted magnetic flux ropes are reservoirs of free magnetic energy. In a highly-conducting plasma such as the solar corona, energy release through multiple magnetic reconnections can be modelled as a helicity-conserving relaxation to a minimum energy state. One possible trigger for this relaxation is the ideal kink instability in a twisted flux rope. We show that this provides a good description for confined solar flares, and develop from idealised cylindrical models to realistic models of coronal loops. Using 3D magnetohydrodynamic simulations combined with test-particle simulations of non-thermal electrons and ions, we predict multiple observational signatures of such flares. We then show how interactions and mergers of flux ropes can release free magnetic energy, using relaxation theory to complement simulations of merging-compression formation in spherical tokamaks and heating avalanches in the solar corona.

Authors:Diogo Capelo, Ilídio Lopes

Abstract: The helium flash, occurring in stars of 0.6-2.0 M$_\odot$ at the end of the red giant branch, is not observable via optical means due to the energy of the process being used to lift the core out of degeneracy. Neutrinos, which are linked to the ignition of reactions triggered during the flash and serve as the only cooling process in the inert core, can help characterize changes in internal structure. In this work, we create 18 stellar models across three mass and six metallicity values, chosen in the context of the stellar abundance problem, to compare the evolutionary path up to and probe the helium flash by conducting a detailed study of neutrino emission throughout this crucial phase of stellar evolution. We demonstrate how thermal neutrino emissions could have an imprint on global asteroseismic parameters and use them as an additional tool to infer the impact of compositional changes. We find that a precision of 0.3 $\mu$Hz in the determination of $\Delta \nu$ is enough to distinguish between between the two most prominent solar composition models and confirm that asteroseismic observation can be enough to classify a star as undergoing the process of helium subflashes. We also predict nuclear neutrino emission fluxes and their evolution for all relevant sources.

Authors:Wei-Min Liu, Long Jiang, Wen-Cong Chen, Xiang-Dong Li

Abstract: The disc instability mechanism (DIM) is widely accepted to account for the transient behaviour of dwarf novae (DNe), which experience short outbursts separated by long quiescence. The duty cycle (the ratio between the outburst duration and the recurrence time) determines the amount of accreted mass by the white dwarf (WDs) during outbursts, thus playing an important role in the long-term binary evolution. Employing the code of Modules for Experiments in Stellar Astrophysics, we systemically investigate the influence of the duty cycles on the evolution of DNe and the mass growth of accreting carbon-oxygen (CO) WDs. Our calculations show that, while the DIM can considerably influence the accretion process, efficient WD-mass growth requires a particular range of the duty cycle. For WDs with the initial masses of 0.6, 0.7 and 1.1 $M_\odot$, these duty cycles are 0.006$\,\leq$$d$$\,\leq$0.007, $d$\,=\,0.005 and $d$\,=\,0.003, and the accumulated mass of the WDs can reach 0.1, 0.13 and 0.21 $M_\odot$, respectively. In all of our simulations, no CO WDs can grow their masses to the explosion mass of Type Ia supernovae of about $1.38~M_\odot$. Because of a much short timescale of the outburst state, the final donor-star masses and orbital periods are insensitive to the duty cycles. Therefore, we propose that the DIM in DNe could alleviate the WD mass problem to some extent.

Authors:Kieran A. Stuart, Scott G. Gregory

Abstract: The large-scale magnetic fields of several pre-main sequence (PMS) stars have been observed to be simple and axisymmetric, dominated by tilted dipole and octupole components. The magnetic fields of other PMS stars are highly multipolar and dominantly non-axisymmetric. Observations suggest that the magnetic field complexity increases as PMS stars evolve from Hayashi to Henyey tracks in the Hertzsprung--Russell diagram. Independent observations have revealed that X-ray luminosity decreases with age during PMS evolution, with Henyey track PMS stars having lower fractional X-ray luminosities ($L_\textrm{X}/L_*$) compared to Hayashi track stars. We investigate how changes in the large-scale magnetic field topology of PMS stars influences coronal X-ray emission. We construct coronal models assuming pure axisymmetric multipole magnetic fields, and magnetic fields consisting of a dipole plus an octupole component only. We determine the closed coronal emitting volume, over which X-ray emitting plasma is confined, using a pressure balance argument. From the coronal volumes we determine X-ray luminosities. We find that $L_\textrm{X}$ decreases as the degree $\ell$ of the multipole field increases. For dipole plus octupole magnetic fields we find that $L_\textrm{X}$ tends to decrease as the octupole component becomes more dominant. By fixing the stellar parameters at values appropriate for a solar mass PMS star, varying the magnetic field topology results in two orders of magnitude variation in $L_\textrm{X}$. Our results support the idea that the decrease in $L_\textrm{X}$ as PMS stars age can be driven by an increase in the complexity of the large-scale magnetic field.

Authors:B. Fuhrmeister, S. Czesla, J. H. M. M. Schmitt, P. C. Schneider, J. A. Caballero, S. V. Jeffers, E. Nagel, D. Montes, M. C. Gálves Ortiz, A. Reinerns, I. Ribas, A. Quirrenbach, P. J. Amado, Th. Henning, N. Lodieu, P. Martín-Fernández, J. C. Morales, P. Schöfer, W. Seifert, M. Zechmeister

Abstract: The hydrogen Paschen lines are known activity indicators, but studies of them in M~dwarfs during quiescence are as rare as their reports in flare studies. This situation is mostly caused by a lack of observations, owing to their location in the near-infrared regime, which is covered by few high-resolution spectrographs. We study the Pa$\beta$ line, using a sample of 360 M~dwarfs observed by the CARMENES spectrograph. Descending the spectral sequence of inactive M~stars in quiescence, we find the Pa$\beta$ line to get shallower until about spectral type M3.5 V, after which a slight re-deepening is observed. Looking at the whole sample, for stars with H$\alpha$ in absorption, we find a loose anti-correlation between the (median) pseudo-equivalent widths (pEWs) of H$\alpha$ and Pa$\beta$ for stars of similar effective temperature. Looking instead at time series of individual stars, we often find correlation between pEW(H$\alpha$) and pEW(Pa$\beta$) for stars with H$\alpha$ in emission and an anti-correlation for stars with H$\alpha$ in absorption. Regarding flaring activity, we report the automatic detection of 35 Paschen line flares in 20 stars. Additionally we found visually six faint Paschen line flares in these stars plus 16 faint Paschen line flares in another 12 stars. In strong flares, Paschen lines can be observed up to Pa 14. Moreover, we find that Paschen line emission is almost always coupled to symmetric H$\alpha$ line broadening, which we ascribe to Stark broadening, indicating high pressure in the chromosphere. Finally we report a few Pa$\beta$ line asymmetries for flares that also exhibit strong H$\alpha$ line asymmetries.

Authors:Daniela Boneva, Georgi Latev, Svetlana Boeva, Krasimira Yankova, Radoslav Zamanov

Abstract: We present observations of the intranight brightness variability of CR Boo, a member of the AM CVn stars group. The observational data are obtained with the 2m telescope of the Rozhen National Astronomical Observatory and the 60 cm telescope of the Belogradchik Observatory, Bulgaria, in BVR bands. We report the appearance of superhumps, with an amplitude from 0.08 to 0.25 mag, when the maximum brightness reaches the magnitude 14.08 in the V band, and 14.13 in the B band. A secondary maximum of each superhump is detected with the same periodicity as the superhumps: Psh = 24.76 - 24.92 min. In our results, the post maxima are shifted in time from $\approx 7.62$ min to $\approx 16.35$ min in different nights, with an amplitude of $\approx 0.06 - 0.09$ mag and an amplitude difference of $\approx 0.035$ mag towards the superhumps' maximum. We find a correlation of the post maxima with the accretion processes at the outer side of the disc.

Authors:Yu Wang, Sofya Alexeeva, Feng Wang, Ling Liu, Yong Wu, JianGuo Wang, Gang Zhao, Svetlana A. Yakovleva, Andrey K. Belyaev

Abstract: Utilizing a simplified quantum model approach, the low-energy inelastic collision processes between yttrium atoms (ions) and hydrogen atoms have been studied. Rate coefficients corresponding to the mutual neutralization, ion-pair formation, excitation, and de-excitation processes for the above collision systems have been provided in the temperature range of 1000-10000K. 3 ionic states and 73 covalent states are considered in calculations for the collisions of yttrium atoms with hydrogen atoms, which include 6 molecular symmetries and 4074 partial inelastic reaction processes. For the collisions of yttrium ions with hydrogen atoms, 1 ionic state and 116 covalent states are included, which related to 3 molecular symmetries and 13572 partial inelastic collision processes. It is found that the rate coefficients for the mutual neutralization process have a maximum at T = 6000K, which is an order of magnitude higher than those of other processes. Notably, the positions of optimal windows for the collisions of yttrium atoms and ions with hydrogen atoms are found near electronic binding energy -2eV (Y) and -4.4eV (Y$^+$), respectively. The scattering channels located in or near these optimal windows have intermediate-to-large rate coefficients (greater than $10^{-12}$ cm$^3$s$^{-1}$). The reported data should be useful in the study of non-local thermodynamic equilibrium modeling.

Authors:Chaowei Jiang, Xueshang Feng, Xinkai Bian, Peng Zou, Aiying Duan, Xiaoli Yan, Qiang Hu, Wen He, Xinyi Wang, Pingbing Zuo, Yi Wang

Abstract: Solar eruptions are the leading driver of space weather, and it is vital for space weather forecast to understand in what conditions the solar eruptions can be produced and how they are initiated. The rotation of sunspots around their umbral center has long been considered as an important condition in causing solar eruptions. To unveil the underlying mechanisms, here we carried out a data-driven magnetohydrodynamics simulation for the event of a large sunspot with rotation for days in solar active region NOAA 12158 leading to a major eruption. The photospheric velocity as recovered from the time sequence of vector magnetograms are inputted directly at the bottom boundary of the numerical model as the driving flow. Our simulation successfully follows the long-term quasi-static evolution of the active region until the fast eruption, with magnetic field structure consistent with the observed coronal emission and onset time of simulated eruption matches rather well with the observations. Analysis of the process suggests that through the successive rotation of the sunspot the coronal magnetic field is sheared with a vertical current sheet created progressively, and once fast reconnection sets in at the current sheet, the eruption is instantly triggered, with a highly twisted flux rope originating from the eruption. This data-driven simulation stresses magnetic reconnection as the key mechanism in sunspot rotation leading to eruption.

Authors:M. Waidele, Junwei Zhao

Abstract: Several recent studies utilizing different helioseismic methods have confirmed the presence of large-scale vorticity waves known as solar Rossby waves within the Sun. Rossby waves are distinct from acoustic waves, typically with longer periods and lifetimes; and their general properties, even if only measured at the surface, may be used to infer properties of the deeper convection zone, such as the turbulent viscosity and entropy gradients which are otherwise difficult to observe. In this study, we utilize $12~$years of inverted subsurface velocity fields derived from the SDO/HMI's time--distance and ring-diagram pipelines to investigate the propoerty of the solar equatorial Rossby waves. By covering the maximum and the decline phases of Solar Cycle 24, these datasets enable a systematic analysis of any potential cycle dependence of these waves. Our analysis provides evidence of a correlation between the average power of equatorial Rossby waves and the solar cycle, with stronger Rossby waves during the solar maximum and weaker waves during the minimum. Our result also shows that the frequency of the Rossby waves is lower during the magnetic active years, implying a larger retrograde drift relative to the solar rotation. Although the underlying mechanism that enhances the Rossby wave power and lowers its frequency during the cycle maximum is not immediately known, this observation has the potential to provide new insights into the interaction of large-scale flows with the solar cycle.

Authors:Enrique Miguel García-Zamora, Santiago Torres, Alberto Rebassa-Mansergas

Abstract: The third data release of Gaia has provided approximately 220 million low resolution spectra. Among these, about 100,000 correspond to white dwarfs. The magnitude of this quantity of data precludes the possibility of performing spectral analysis and type determination by human inspection. In order to tackle this issue, we explore the possibility of utilising a machine learning approach, based on a Random Forest algorithm. We aim to analyze the viability of the Random Forest algorithm for the spectral classification of the white dwarf population within 100 pc from the Sun, based on the Hermite coefficients of Gaia spectra. We utilized the assigned spectral type from the Montreal White Dwarf Database for training and testing our Random Forest algorithm. Once validated, our algorithm model is applied to the rest of unclassified white dwarfs within 100 pc. First, we started by classifying the two major spectral type groups of white dwarfs: hydrogen-rich (DA) and hydrogen-deficient (non-DA). Next, we explored the possibility of classifying the various spectral subtypes, including in some cases the secondary spectral types. Our Random Forest classification presented a very high recall (>80%) for DA and DB white dwarfs, and a very high precision (>90%) for DB, DQ and DZ white dwarfs. As a result we have assigned a spectral type to 9,446 previously unclassified white dwarfs: 4,739 DAs, 76 DBs (60 of them DBAs), 4,437 DCs, 132 DZs and 62 DQs (9 of them DQpec). Despite the low resolution of Gaia spectra, the Random Forest algorithm applied to the Gaia spectral coefficients proves to be a highly valuable tool for spectral classification.

Authors:Giulia C. Cinquegrana, Meridith Joyce, Amanda I. Karakas

Abstract: The minimum initial mass required for a star to explode as an Fe core collapse supernova, typically denoted $M_\text{mas}$, is an important quantity in stellar evolution because it defines the border between intermediate mass and massive stellar evolutionary paths. The precise value of $M_\text{mas}$ carries implications for models of galactic chemical evolution and the calculation of star formation rates. Despite the fact that stars with super solar metallicities are commonplace within spiral and some giant elliptical galaxies, there are currently no studies of this mass threshold in super metal-rich models with $Z>0.05$. Here, we study the minimum mass necessary for a star to undergo an Fe core collapse supernova when its initial metal content falls in the range $2.5\times 10^{-3} \leq Z \leq 0.10$. Although an increase in initial $Z$ corresponds to an increase in the Fe ignition threshold for $Z \approx 1\times 10^{-3}$ to $Z\approx0.04$, we find that there is a steady reversal in trend that occurs for $Z > 0.05$. Our super metal-rich models thus undergo Fe core collapse at lower initial masses than those required at solar metallicity. Our results indicate that metallicity--dependent curves extending to $Z=0.10$ for the minimum Fe ignition mass should be utilised in galactic chemical evolution simulations to accurately model supernovae rates as a function of metallicity, particularly for simulations of metal-rich spiral and elliptical galaxies.

Authors:D. Weßmayer, N. Przybilla, A. Ebenbichler, P. Aschenbrenner, K. Butler

Abstract: Aims. The evolutionary status of the blue supergiant Sher 25 and its membership to the massive cluster NGC 3603 are investigated. Methods. A hybrid non-LTE (local thermodynamic equilibrium) spectrum synthesis approach is employed to analyse a high-resolution optical spectrum of Sher 25 and five similar early B-type comparison stars in order to derive atmospheric parameters and elemental abundances. Fundamental stellar parameters are determined by considering stellar evolution tracks, Gaia Data Release 3 (DR3) data and complementary distance information. Interstellar reddening and the reddening law along the sight line towards Sher 25 are constrained employing UV photometry for the first time in addition to optical and infrared data. The distance to NGC 3603 is reevaluated based on Gaia DR3 data of the innermost cluster O-stars. Results. The spectroscopic distance derived from the quantitative analysis implies that Sher 25 lies in the foreground of NGC 3603, which is found to have a distance of $d_\mathrm{NGC 3603}$ = 6250$\pm$150 pc. A cluster membership is also excluded as the hourglass nebula is unaffected by the vigorous stellar winds of the cluster stars and from the different excitation signatures of the hourglass nebula and the nebula around NGC 3603. Sher 25 turns out to have a luminosity of log L/L$_\odot$ = 5.48$\pm$0.14, equivalent to that of a $\sim$27 $M_\odot$ supergiant in a single-star scenario, which is about half of the mass assumed so far, bringing it much closer in its characteristics to Sk-69{\deg}202, the progenitor of SN 1987A. Sher 25 is significantly older than NGC 3603. Further arguments for a binary (merger) evolutionary scenario of Sher 25 are discussed.

Authors:Quan Wang, Mei Zhang, Shangbin Yang, Xiao Yang, Xiaoshuai Zhu

Abstract: Magnetic helicity is an important concept in solar physics, with a number of theoretical statements pointing out the important role of magnetic helicity in solar flares and coronal mass ejections (CMEs). Here we construct a sample of 47 solar flares, which contains 18 no-CME-associated confined flares and 29 CME-associated eruptive flares. We calculate the change ratios of magnetic helicity and magnetic free energy before and after these 47 flares. Our calculations show that the change ratios of magnetic helicity and magnetic free energy show distinct different distributions in confined flares and eruptive flares. The median value of the change ratios of magnetic helicity in confined flares is $-0.8$%, while this number is $-14.5$% for eruptive flares. For the magnetic free energy, the median value of the change ratios is $-4.3$% for confined flares, whereas this number is $-14.6$% for eruptive flares. This statistical result, using observational data, is well consistent with the theoretical understandings that magnetic helicity is approximately conserved in the magnetic reconnection, as shown by confined flares, and the CMEs take away magnetic helicity from the corona, as shown by eruptive flares.

Authors:Sihui Zhong, Valery M. Nakariakov, Yuhu Miao, Libo Fu, Ding Yuan

Abstract: The energy balance in the corona of the Sun is the key to the long-standing coronal heating dilemma, which could be potentially revealed by observational studies of decayless kink oscillations of coronal plasma loops. A bundle of very long off-limb coronal loops with the length of $736\pm80$ Mm and a lifetime of about 2 days are found to exhibit decayless kink oscillations. The oscillations were observed for several hours. The oscillation amplitude was measured at 0.3-0.5 Mm, and the period at 28-33 min. The existence of 30-min periodicity of decayless kink oscillations indicates that the mechanism compensating the wave damping is still valid in such a massive plasma structure. It provides important evidence for the non-resonant origin of decayless kink oscillations with 2-6min periods, i.e., the lack of their link with the leakage of photospheric and chromospheric oscillations into the corona and the likely role of the broadband energy sources. Magnetohydrodynamic seismology based on the reported detection of the kink oscillation, with the assistance of the differential emission measure analysis and a background coronal model provides us with a comprehensive set of plasma and magnetic field diagnostics, which is of interest as input parameters of space weather models.

Authors:O. Vincent, M. A. Barstow, S. Jordan, C. Mander, P. Bergeron, P. Dufour

Abstract: The latest Gaia data release in July 2022, DR3, added a number of important data products to those available in earlier releases, including radial velocity data, information on stellar multiplicity and XP spectra of a selected sample of stars. While the normal Gaia photometry (G, GBP and GRP bands) and astrometry can be used to identify white dwarfs with high confidence, it is much more difficult to parameterise the stars and determine the white dwarf spectral type from this information alone. The availability of the XP spectra and synthetic photometry presents an opportunity for more detailed spectral classification and measurement of effective temperature and surface gravity of Gaia white dwarfs. A magnitude limit of G < 17.6 was applied to the routine production of XP spectra for Gaia sources, which would have excluded most white dwarfs. We created a catalogue of 100,000 high-quality white dwarf identifications for which XP spectra were processed, with a magnitude limit of G < 20.5. Synthetic photometry was computed for all these stars, from the XP spectra, in Johnson, SDSS and J-PAS, published as the Gaia Synthetic Photometry Catalogue - White Dwarfs (GSPC-WD). We have now taken this catalogue and applied machine learning techniques to provide a classification of all the stars from the XP spectra. We have then applied an automated spectral fitting programme, with chi-squared minimisation, to measure their physical parameters (effective temperature and log g) from which we can estimate the white dwarf masses and radii. We present the results of this work, demonstrating the power of being able to classify and parameterise such a large sample of 100, 000 stars. We describe what we can learn about the white dwarf population from this data set. We also explore the uncertainties in the process and the limitations of the data set.

Authors:I. Rogachevskii BGU, N. Kleeorin BGU

Abstract: Solar, stellar and galactic large-scale magnetic fields are originated due to a combined action of non-uniform (differential) rotation and helical motions of plasma via mean-field dynamos. Usually, nonlinear mean-field dynamo theories take into account algebraic and dynamic quenching of alpha effect and algebraic quenching of turbulent magnetic diffusivity. However, these theories do not take into account a feedback of the mean magnetic field on the background turbulence (with a zero mean magnetic field). Our analysis using the budget equation for the total (kinetic plus magnetic) turbulent energy, which takes into account the feedback of the generated mean magnetic field on the background turbulence, has shown that a nonlinear dynamo number decreases with increase of the mean magnetic field for a forced turbulence, and a shear-produced turbulence and a convective turbulence. This implies that mean-field dynamo instability is always saturated.

Authors:Shi-Jie Gao, Xiang-Dong Li

Abstract: Helium white dwarfs (HeWDs) are thought to form from low-mass red giant stars experiencing binary interaction. Because the helium core mass of a red giant star is closely related to the stellar radius, there exists well-known relation between the orbital period ($P_{\rm orb}$) and the mass ($M_{\rm WD}$) of the HeWDs, which is almost independent of the type of the companion star. Traditional derivation of the $M_{\rm WD}$-$P_{\rm orb}$ relation generally neglected the effect of wind mass loss from the red giants, while observations show that wind mass loss from red giants in binary systems is systematically higher than that from isolated stars. In this work, we calculate binary evolution with tidally enhanced stellar wind (TEW) and find that it causes significantly scatter of the traditional $M_{\rm WD}$-$P_{\rm orb}$ relation. The TEW can prevent the red giants from overflowing their Roche lobes and slow down the growth of the helium core, leaving a lower-mass HeWD for given orbital period. This scenario may account for some of the HeWD binaries that deviate from the traditional $M_{\rm WD}$-$P_{\rm orb}$ relation. However, we point out that observations of more HeWD binaries in wide orbits are needed to test the TEW model and to constrain the enhanced wind factor.

Authors:Jeremy A. Grajeda, Laura E. Boucheron, Michael S. Kirk, Andrew Leisner, C. Nick Arge

Abstract: This paper presents an intramethod ensemble for coronal hole (CH) detection based on the Active Contours Without Edges (ACWE) segmentation algorithm. The purpose of this ensemble is to develop a confidence map that defines, for all on disk regions of a Solar extreme ultraviolet (EUV) image, the likelihood that each region belongs to a CH based on that region's proximity to, and homogeneity with, the core of identified CH regions. CHs are regions of open magnetic field lines, resulting in high speed solar wind. Accurate detection of CHs is vital for space weather prediction. By relying on region homogeneity, and not intensity (which can vary due to various factors including line of sight changes and stray light from nearby bright regions), to define the final confidence of any given region, this ensemble is able to provide robust, consistent delineations of the CH regions. Using the metrics of global consistency error (GCE), local consistency error (LCE), intersection over union (IOU), and the structural similarity index measure (SSIM), the method is shown to be robust to different spatial resolutions and different intensity resolutions. Furthermore, using the same metrics, the method is shown to be robust across short timescales, indicating self-consistent segmentations. Finally, the accuracy of the segmentations and confidence maps are validated by considering the skewness (i.e., unipolarity) of the underlying magnetic field.

Authors:Alexander N. Shabalin, Evgeniia P. Ovchinnikova, Yuri E. Charikov

Abstract: We analyzed changes in the height of the coronal hard X-ray (HXR) source for flares SOL2013-05-13T01:50 and SOL2013-05-13T15:51. Analysis of the Reuven Ramaty High Energy Solar Spectroscopic Imager data revealed the downward motion of the HXR source and the separation of the sources by energy and height. In the early stages of the flares, a negative correlation was found between the HXR source area in the corona and HXR flux. For the SOL2013-05-13T15:51 event, an increasing trend in the time delay spectra at the footpoints was obtained. For both events, the spectra of the time delays in the coronal HXR source showed a decreasing trend across the energies in certain flare phases. To interpret the observed phenomena, we considered a flare model of collapsing traps and calculated the distribution functions of accelerated electrons along the magnetic loop using a nonstationary relativistic kinetic equation. This approach considers betatron and Fermi first-order acceleration mechanisms. The increasing trend of the time delay spectra at the footpoints was explained by the high mirror ratio in the magnetic loop and betatron acceleration mechanism. The observed features in the spatial and temporal behavior of the HXR sources, such as the negative correlation between the HXR source area and HXR flux, can be interpreted by the collapsing trap model.

Authors:Purvi Udhwani, Arpit Kumar Shrivastav, Ritesh Patel

Abstract: SiRGraF Integrated Tool for Coronal dynaMics (SITCoM) is based on Simple Radial Gradient Filter (SiRGraF) used to filter the radial gradient in the white-light coronagraph images and bring out dynamic structures. SITCoM has been developed in Python and integrated with SunPy and can be installed by users with the command pip install sitcom. This enables the user to pass the white-light coronagraph data to the tool and generate radially filtered output with an option to save in various formats as required. We have implemented the functionality of tracking the transients such as coronal mass ejections (CMEs), outflows, plasma blobs, etc., using height-time plots and deriving their kinematics. In addition, SITCoM also supports oscillation and waves studies such as for streamer waves. This is done by creating a distance-time plot at a user-defined location (artificial slice) and fitting a sinusoidal function to derive the properties of waves, such as time period, amplitude, and damping time (if any). We provide the provision to manually or automatically select the data points to be used for fitting. SITCoM is a tool to analyze some properties of coronal dynamics quickly. We present an overview of the SITCoM with the applications for deriving coronal dynamics' kinematics and oscillation properties. We discuss the limitations of this tool along with prospects for future improvement.

Authors:Ze-Xi Niu, Ning-Chen Sun, Justyn R. Maund, Yu Zhang, Rui-Ning Zhao, Ji-Feng Liu

Abstract: As one of the closest supernovae (SNe) in the last decade, SN 2023ixf is an unprecedented target to investigate the progenitor star that exploded. However, there is still significant uncertainty in the reported progenitor properties. In this work, we present a detailed study of the progenitor of SN 2023ixf with two independent analyses. We first modelled its spectral energy distribution (SED) based on Hubble Space Telescope optical, Spitzer mid-infrared (IR), and ground-based near-IR data. We find that stellar pulsation and circumstellar extinction have great impacts on SED fitting, and the result suggests a relatively massive red supergiant (RSG) surrounded by C-rich dust with an initial mass of 16.2--17.4 Msun. The corresponding mass-loss rate estimate is 1e-5 Msun/yr. We also derived the star formation history of the SN environment based on resolved stellar populations, and the most recent star-forming epoch corresponds to a progenitor initial mass of 17--19 Msun, in agreement with that from our SED fitting. Therefore, we conclude that the progenitor of SN 2023ixf is close to the high-mass end for Type II SN progenitors.

Authors:M. Temmer, C. Scolini, I. G. Richardson, S. G. Heinemann, E. Paouris, A. Vourlidas, M. M. Bisi, writing teams, :, N. Al-Haddad, T. Amerstorfer, L. Barnard, D. Buresova, S. J. Hofmeister, K. Iwai, B. V. Jackson, R. Jarolim, L. K. Jian, J. A. Linker, N. Lugaz, P. K. Manoharan, M. L. Mays, W. Mishra, M. J. Owens, E. Palmerio, B. Perri, J. Pomoell, R. F. Pinto, E. Samara, T. Singh, D. Sur, C. Verbeke, A. M. Veronig, B. Zhuang

Abstract: The ISWAT clusters H1+H2 have a focus on interplanetary space and its characteristics, especially on the large-scale co-rotating and transient structures impacting Earth. SIRs, generated by the interaction between high-speed solar wind originating in large-scale open coronal magnetic fields and slower solar wind from closed magnetic fields, are regions of compressed plasma and magnetic field followed by high-speed streams that recur at the ca. 27 day solar rotation period. Short-term reconfigurations of the lower coronal magnetic field generate flare emissions and provide the energy to accelerate enormous amounts of magnetised plasma and particles in the form of CMEs into interplanetary space. The dynamic interplay between these phenomena changes the configuration of interplanetary space on various temporal and spatial scales which in turn influences the propagation of individual structures. While considerable efforts have been made to model the solar wind, we outline the limitations arising from the rather large uncertainties in parameters inferred from observations that make reliable predictions of the structures impacting Earth difficult. Moreover, the increased complexity of interplanetary space as solar activity rises in cycle 25 is likely to pose a challenge to these models. Combining observational and modeling expertise will extend our knowledge of the relationship between these different phenomena and the underlying physical processes, leading to improved models and scientific understanding and more-reliable space-weather forecasting. The current paper summarizes the efforts and progress achieved in recent years, identifies open questions, and gives an outlook for the next 5-10 years. It acts as basis for updating the existing COSPAR roadmap by Schrijver+ (2015), as well as providing a useful and practical guide for peer-users and the next generation of space weather scientists.

Authors:A. Z. Bonanos, G. Maravelias, M. Yang, F. Tramper, S. de Wit, E. Zapartas, K. Antoniadis, E. Christodoulou, G. Munoz-Sanchez

Abstract: Episodic mass loss is not understood theoretically, neither accounted for in state-of-the-art models of stellar evolution, which has far-reaching consequences for many areas of astronomy. We introduce the ERC-funded ASSESS project (2018-2024), which aims to determine whether episodic mass loss is a dominant process in the evolution of the most massive stars, by conducting the first extensive, multi-wavelength survey of evolved massive stars in the nearby Universe. It hinges on the fact that mass-losing stars form dust and are bright in the mid-infrared. We aim to derive physical parameters of $\sim$1000 dusty, evolved massive stars in $\sim$25 nearby galaxies and estimate the amount of ejected mass, which will constrain evolutionary models, and quantify the duration and frequency of episodic mass loss as a function of metallicity. The approach involves applying machine-learning algorithms to select dusty, luminous targets from existing multi-band photometry of nearby galaxies. We present the first results of the project, including the machine-learning methodology for target selection and results from our spectroscopic observations so far. The emerging trend for the ubiquity of episodic mass loss, if confirmed, will be key to understanding the explosive early Universe and will have profound consequences for low-metallicity stars, reionization, and the chemical evolution of galaxies.

Authors:Xinkai Bian, Chaowei Jiang, Xueshang Feng, Pingbing Zuo, Yi Wang

Abstract: Recently we established a fundamental mechanism of solar eruption initiation, in which an eruption can be initiated from a bipolar field through magnetic reconnection in the current sheet (CS) that is formed slowly in the core field as driven by photospheric shearing motion. Here using a series of fully 3D MHD simulations with a range of different photospheric magnetic flux distributions, we extended this fundamental mechanism to the quadrupolar magnetic field containing a null point above the core field, which is the basic configuration of the classical breakout model. As is commonly believed, in such multipolar configuration, the reconnection triggered in the CS originated at the null point (namely, the breakout reconnection) plays the key role in eruption initiation by establishing a positive feedback-loop between the breakout reconnection and the expansion of the core field. However, our simulation showed that the key of eruption initiation in such multipolar configuration remains to be the slow formation of the CS in the sheared core rather than the onset of fast breakout reconnection. The breakout reconnection only helps the formation of the core CS by letting the core field expand faster, but the eruption cannot occur when the bottom surface driving is stopped well before the core CS is formed, even though the fast reconnection has already been triggered in the breakout CS. This study clarified the role of breakout reconnection and confirmed formation of the core CS as the key to the eruption initiation in a multipolar magnetic field.

Authors:Tatiana V. Demidova, Vladimir P. Grinin

Abstract: One of the early hypotheses about the origin of FUOR outbursts explains them by the fall of gas clumps from the remnants of protostellar clouds onto protoplanetary disks surrounding young stars (Hartmann and Kenyon 1985). To calculate the consequences of such an event we make 3D hydrodynamic simulations by SPH method. It is shown that the fall of the clump on the disk in the vicinity of the star actually causes a burst of the star's accretion activity, resembling in its characteristics the flares of known FUORs. In the region of incidence, an inhomogeneous gas ring is formed, which is inclined relative to the outer disk. During several revolutions around the star, this ring combines with the inner disk and forms a tilted disk. In the process of evolution, the inner disk expands, and its inclination relative to the outer disk decreases. After 100 revolutions, the angle of inclination is a few degrees. This result is of interest in connection with the discovery in recent years of protoplanetary disks, the inner region of which is inclined relative to the outer one. Such structures are usually associated with the existence in the vicinity of a star of a massive body (planet or brown dwarf), whose orbit is inclined relative to the plane of the disk. The results of our modeling indicate the possibility of an alternative explanation for this phenomenon.

Authors:Pallavi Saraf IIA, Thirupathi Sivarani IIA

Abstract: Here, we delineate a comprehensive abundance analysis of four $r$-process enhanced metal-poor stars observed with HORuS spectrograph on a 10-m class telescope, GTC. The high signal-to-noise ratio at $R \approx 25000$ spectral resolution allowed us to detect 16 light and 20 neutron-capture elements along with Th in two stars. Four of our program stars show signatures of mixing in their atmosphere. Through detailed abundance analysis of four $r$-process enhanced stars together with already identified $r$-process-rich stars in literature, we probe the production sites of neutron-capture elements. The [Zr/Eu] ratio as a function of metallicity shows the evidence of multiple channels for the production of $r$-process. Thorium to first and second $r$-process peak elements ratios also support the similar non-universality of neutron-capture elements. An increased sample of $r$-process enhanced stars will enable us understand different formation channels of neutron capture elements. Using the kinematic analysis, we found the clues of accretion for two of our program stars.

Authors:P. J. Storey, R. P. Dufresne, G. Del Zanna

Abstract: We use the Breit Pauli $R$-matrix method to calculate accurate energies and radiative data for states in C I up to $n$=30 and with $l\le 3$. We provide the full dataset of decays to the five 2s$^2$2p$^2$ ground configuration states $^3$P$_{0,1,2}$, $^1$D$_2$, $^1$S$_0$. This is the first complete set of data for transitions from $n\ge 5$. We compare oscillator strengths and transition probabilities with the few previously calculated values for such transitions, finding generally good agreement (within 10%) with the exception of values recently recommended by NIST, where significant discrepancies are found. We then calculate spectral line intensities originating from the Rydberg states using typical chromospheric conditions and assuming LTE, and compare them with well-calibrated SOHO SUMER UV spectra of the quiet Sun. The relative intensities of the Rydberg series are in excellent agreement with observation, which provides firm evidence for the identifications and blends of nearly 200 UV lines. Such comparison also resulted in a large number of new identifications of C I lines in the spectra. We also estimate optical depth effects and find that these can account for much of the absorption noted in the observations. The atomic data can be applied to model a wide range of solar and astrophysical observations.

Authors:Anju Panthi, Annapurni Subramaniam, Kaushar Vaidya, Vikrant Jadhav, Sharmila Rani, Sivarani Thirupathi, Sindhu Pandey

Abstract: Blue metal-poor (BMP) stars are the main-sequence stars that appear bluer and more luminous than normal turn-off stars of metal-poor globular clusters. They are believed to be either field blue straggler stars (FBSS) formed via post-mass transfer mechanism or accreted from dwarf satellite galaxies of the Milky Way. A significant fraction of BMP stars are discovered to be potential binaries. We observed 27 BMP stars using UVIT/\textit{AstroSat} in two FUV filters, F148W and F169M. We report the discovery of white dwarf (WD) companions of 12 BMP stars for the first time. The WD companions have estimated temperatures T$_{eff}$ $\sim$10500 $-$ 18250 K, and masses 0.17 M$_{\odot}$ $-$ 0.8 M$_{\odot}$. Based on [Fe/H] and space velocity, we group the 12 BMP/FBSS stars as the thick disk (5) and halo (5), whereas two stars appear to be in-between. All the 5 thick disk BMP/FBSS have extremely low-mass (M $<$ 0.2 M$_{\odot}$) WDs as companions, whereas the 5 halo BMP/FBSS have low (0.2 M$_{\odot}$ $<$ M $<$ 0.4 M$_{\odot}$), normal (0.4 M$_{\odot}$ $<$ M $<$ 0.6M$_{\odot}$), and high mass (M $>$ 0.6 M$_{\odot}$) WD companions. Our analysis suggests that at least $\sim$44 $\%$ of BMP stars are FBSS, and these stars hold the key to understand the details of mass transfer, binary properties, and chemical enrichment among the FBSS.

Authors:R. K. Zamanov, V. Marchev, J. Marti, G. Y. Latev

Abstract: Pre-outburst signal (a decrease of the optical brightness) just before the outburst is clearly detected in the observations of the T CrB obtained before and during the 1946 outburst. A similar decrease is also visible in the light curve of RS Oph during the 2021 outburst. We suppose that this is due to formation of a thick, dense envelope around the white dwarf, and we estimate its size (1000 - 2000 km), mass (5.10$^{-8}$ - 6.10$^{-7}$ M$_\odot$) and average density (5 - 16 g cm$^{-3}$).

Authors:Oliver Pearce, Sergei N. Yurchenko, Jonathan Tennyson

Abstract: Comprehensive and accurate rovibronic line lists for the X $^{1}\Sigma^{+}$ and A $^{1}\Pi$ states of $^{12}$C$^{1}$H$^{+}$ and $^{13}$C$^{1}$H$^{+}$ which should be applicable up to temperatures of 5000 K are presented. Available empirical potential energy curves and high-level ab initio dipole and transition dipole moment curves are used with the program LEVEL to compute rovibronic energy levels and Einstein $A$ coefficients. $\Lambda$-doubling is incorporated into the energy levels and $A$-coefficients involving the A $^{1}\Pi$ state using an empirical method. For $^{12}$C$^{1}$H$^{+}$, line positions are improved by using both laboratory and astronomical observational spectra as input to the MARVEL procedure. The $^{12}$C$^{1}$H$^{+}$ line list contains 1505 states and 34194 transitions over the frequency range of 0 - 33010 cm$^{-1}$ ($\lambda > 300$ nm). Comparisons with observed astronomical and laboratory spectra give very good agreement. The PYT CH$^{+}$ line lists and partition functions are available from the ExoMol database at www.exomol.com.

Authors:Sergei N. Yurchenko, Ryan P. Brady, Jonathan Tennyson, Alexander N. Smirnov, Oleg A. Vasilyev, Victor G. Solomonik

Abstract: Empirical line lists for the open shell molecule $^{89}$Y$^{16}$O (yttrium oxide) and its isotopologues are presented. The line list covers the 6 lowest electronic states: $X {}^{2}\Sigma^{+}$, $A {}^{2}\Pi$, $A' {}^{2}\Delta$, $B {}^{2}\Sigma^{+}$, $C {}^{2}\Pi$ and $D {}^{2}\Sigma^{+}$ up to 60000 cm$^{-1}$ ($<0.167$ $\mu$m) for rotational excitation up to $J = 400.5$. An \textit{ab initio} spectroscopic model consisting of potential energy curves (PECs), spin-orbit and electronic angular momentum couplings is refined by fitting to experimentally determined energies of YO, derived from published YO experimental transition frequency data. The model is complemented by empirical spin-rotation and $\Lambda$-doubling curves and \textit{ab initio} dipole moment and transition dipole moment curves computed using MRCI. The \textit{ab initio} PECs computed using the complete basis set limit extrapolation and the CCSD(T) method with its higher quality provide an excellent initial approximation for the refinement. Non-adiabatic coupling curves for two pairs of states of the same symmetry $A$/$C$ and $B$/$D$ are computed using a state-averaged CASSCF and used to built diabatic representations for the $A {}^{2}\Pi$, $C {}^{2}\Pi$, $B {}^{2}\Sigma^{+}$ and $D {}^{2}\Sigma^{+}$ curves. Calculated lifetimes of YO are tuned to agree well with the experiment, where available. The BRYTS YO line lists for are included into the ExoMol data base (www.exomol.com).

Authors:D. M. Weigt, L. A. Cañizares, S. A. Maloney, S. A. Murray, E. P. Carley, P. T. Gallagher, A. Macario-Rojas, N. Crisp, C. McGrath

Abstract: One of the greatest challenge facing current space weather monitoring operations is forecasting the arrival of coronal mass ejections (CMEs) and Solar Energetic Particles (SEPs) within their Earth-Sun propagation timescales. Current campaigns mainly rely on extreme ultra-violet and white light observations to create forecasts, missing out many potential events that may be hazardous to Earth's infrastructure undetectable at these wavelengths. Here we introduce the SURROUND mission, a constellation of CubeSats each with identical radio spectrometers, and the results of the initial Phase-0 study for the concept. The main goal of SURROUND is to monitor and track solar radio bursts (SRBs), widely utilised as a useful diagnostic for space weather activity, and revolutionise current forecasting capabilities. The Phase-0 study concludes that SURROUND can achieve its mission objectives using 3 - 5 spacecraft using current technologies with feasible SEP and CME forecasting potential: a first for heliospheric monitors.

Authors:S. Gunasekera, J. Adassuriya, I. Madagangoda, K. Werellapatha, K. P. S. C Jayaratne

Abstract: The spectroscopic observations of two novae namely V1065 CEN and V1280 SCO were made by 45 cm Cassegrain telescope in high resolution ($\lambda/\delta\lambda$=22000) at H$\alpha$ (6563 \r{A}) region. V1065 CEN is He/N-type spectra which characterize a broad (Gaussian FWHM 49 \r{A}), saddle shaped and asymmetric H$\alpha$ emission line without prominent P-Cyg absorption component. Completely different H$\alpha$ profile of V1280 SCO shows prominent P-Cyg absorption and narrow emission line (Gaussian FWHM 26 \r{A}) which can be classified as Fe II type nova. The expansion velocities of these two systems measured from the minima of the P-Cyg profiles are close to 2300 km/s for V1065 CEN, and 716 km/s for V1280 SCO. Based on the photometric analysis, the Nova V1065 CEN can be classified as fast (11$<$t${_2}$$<$25) nova. The derived absolute magnitudes at maximum for nova V1065 CEN to be M$_{o,V}$ = -7.58$\pm$0.18 and M$_{o,B}$= -7.75$\pm$0.25 correspond to a distance 8.51$\pm$0.33 kpc. The parameters t$_{2V}$=12 days and t$_{3V}$=14 days of nova V1280 SCO determine that the nova is in between very fast and fast nova. The mean absolute magnitude at maximum is calculated to be M$_{o,V}$=-8.7$\pm$0.1 and the estimated distance to the nova V1280 SCO is 3.2$\pm$0.2 kpc.

Authors:Timo Reinhold, Alexander I. Shapiro, Sami K. Solanki, Gibor Basri

Abstract: The Kepler space telescope leaves a legacy of tens of thousands of stellar rotation period measurements. While many of these stars show strong periodicity, there exists an even bigger fraction of stars with irregular variability for which rotation periods are unknown. As a consequence, many stellar activity studies might be strongly biased toward the behavior of more active stars with measured rotation periods. To at least partially lift this bias, we apply a new method based on the Gradient of the Power Spectrum (GPS). The maximum of the gradient corresponds to the position of the inflection point (IP). It was shown previously that the stellar rotation period $P_{rot}$ is linked to the inflection point period $P_{IP}$ by the simple equation $P_{rot} = P_{IP}/\alpha$, where $\alpha$ is a calibration factor. The GPS method is superior to classical methods (such as auto-correlation functions (ACF)) because it does not require a repeatable variability pattern in the time series. From the initial sample of 142,168 stars with effective temperature $T_{eff}\leq6500K$ and surface gravity $log g\geq4.0$ in the Kepler archive, we could measure rotation periods for 67,163 stars by combining the GPS and the ACF method. We further report the first determination of a rotation period for 20,397 stars. The GPS periods show good agreement with previous period measurements using classical methods, where these are available. Furthermore, we show that the scaling factor $\alpha$ increases for very cool stars with effective temperatures below 4000K, which we interpret as spots located at higher latitudes. We conclude that new techniques (such as the GPS method) must be applied to detect rotation periods of stars with small and more irregular variabilities. Ignoring these stars will distort the overall picture of stellar activity and, in particular, solar-stellar comparison studies.

Authors:Steven R. Cranmer CU Boulder, Momchil E. Molnar CU Boulder, HAO/NCAR

Abstract: The solar atmosphere is known to contain many different types of wavelike oscillation. Waves and other fluctuations (e.g., turbulent eddies) are believed to be responsible for at least some of the energy transport and dissipation that heats the corona and accelerates the solar wind. Thus, it is important to understand the behavior of magnetohydrodynamic (MHD) waves as they propagate and evolve in different regions of the Sun's atmosphere. In this paper, we investigate how MHD waves can affect the overall plasma state when they reflect and refract at sharp, planar interfaces in density. First, we correct an error in a foundational paper (Stein 1971) that affects the calculation of wave energy-flux conservation. Second, we apply this model to reflection-driven MHD turbulence in the solar wind, where the presence of density fluctuations can enhance the generation of inward-propagating Alfven waves. This model reproduces the time-averaged Elsasser imbalance fraction (i.e., ratio of inward to outward Alfvenic power) from several published numerical simulations. Lastly, we model how the complex magnetic field threading the transition region between the chromosphere and corona helps convert a fraction of upward-propagating Alfven waves into fast-mode and slow-mode MHD waves. These magnetosonic waves dissipate in a narrow region around the transition region and produce a sharp peak in the heating rate. This newly found source of heating sometimes exceeds the expected heating rate from Alfvenic turbulence by an order of magnitude. It may explain why some earlier models seemed to require an additional ad-hoc heat source at this location.

Authors:S. M. Andrievsky, S. A. Korotin, K. Werner

Abstract: We have searched for lines of the radioactive element technetium (Tc) in the spectrum of Przybylski's star (HD101065). The nuclei of this chemical element are formed in the slow process of capturing thermalized neutrons. The possible lines of Tc~I are heavily blended. We have synthesized the profile of one resonance line at 4297.06 \AA~, which is also a part of the complex blend, and we arrived at a decision that it is not visible in the spectrum (as was first noted by Ryabchikova), casting doubt on the existence of technetium in the atmosphere of the Przybylski's star. Therefore, based on our calculated combined profile, which has been adjusted to the observed blend profile at ~4297.2 A (that may possibly contain the resonance technetium line 4297.06 A), we reduce the maximum technetium abundance to $\log\epsilon$(Tc/H) = 2.5. This value can be considered only as an upper limit of the technetium abundance in the Przybylski's star.

Authors:Ken J. Shen, Simon Blouin, Katelyn Breivik

Abstract: Gaia's exquisite parallax measurements allowed for the discovery and characterization of the Q branch in the Hertzsprung-Russell diagram, where massive C/O white dwarfs (WDs) pause their dimming due to energy released during crystallization. Interestingly, the fraction of old stars on the Q branch is significantly higher than in the population of WDs that will become Q branch stars or that were Q branch stars in the past. From this, Cheng et al. inferred that ~6% of WDs passing through the Q branch experience a much longer cooling delay than that of standard crystallizing WDs. Previous attempts to explain this cooling anomaly have invoked mechanisms involving super-solar initial metallicities. In this paper, we describe a novel scenario in which a standard composition WD merges with a subgiant star. The evolution of the resulting merger remnant leads to the creation of a large amount of 26Mg, which, along with the existing 22Ne, undergoes a distillation process that can release enough energy to explain the Q branch cooling problem without the need for atypical initial abundances. The anomalously high number of old stars on the Q branch may thus be evidence that mass transfer from subgiants to WDs leads to unstable mergers.

Authors:Casey Y. Lam, Jessica R. Lu

Abstract: There are expected to be $\sim 10^8$ isolated black holes (BHs) in the Milky Way. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with a mass measurement to date. However, its mass is disputed: Lam et al. (2022a,b) measured a lower mass of $1.6 - 4.4 M_\odot$, while Sahu et al. (2022); Mr\'{o}z et al. (2022) measured a higher mass of $5.8 - 8.7 M_\odot$. We re-analyze OB110462, including new data from the Hubble Space Telescope (HST) and re-reduced Optical Gravitational Lensing Experiment (OGLE) photometry. We also re-reduce and re-analyze the HST dataset with newly available software. We find significantly different ($\sim 1$ mas) HST astrometry than Lam et al. (2022a,b) in the de-magnified epochs due to the amount of positional bias induced by a bright star $\sim$0.4 arcsec from OB110462. After modeling the updated photometric and astrometric datasets, we find the lens of OB110462 is a $6.0^{+1.2}_{-1.0} M_\odot$ BH. Future observations with the Nancy Grace Roman Space Telescope, which will have an astrometric precision comparable or better to HST but a field of view $100\times$ larger, will be able to measure hundreds of isolated BH masses via microlensing. This will enable the measurement of the BH mass distribution and improve understanding of massive stellar evolution and BH formation channels.

Authors:H. Nowacki, E. Alecian, K. Perraut, B. Zaire, C. P. Folsom, K. Pouilly, J. Bouvier, R. Manick, G. Pantolmos, A. P. Sousa, C. Dougados, G. A. J. Hussain, S. H. P. Alencar, J. B. Le Bouquin

Abstract: Aims : We aimed at constraining the accretion-ejection phenomena around the strongly-accreting Northern component of the S CrA young binary system (S CrA N) by deriving its magnetic field topology and its magnetospheric properties, and by detecting ejection signatures, if any. Methods : We led a two-week observing campaign on S CrA N with the ESPaDOnS optical spectropolarimeter at the Canada-France-Hawaii Telescope. We recorded 12 Stokes I and V spectra over 14 nights. We computed the corresponding Least-Square Deconvolution (LSD) profiles of the photospheric lines and performed Zeeman-Doppler Imaging (ZDI). We analysed the kinematics of noticeable emission lines, namely He I $\lambda 5876$ and the four first lines of the Balmer series, known to trace the accretion process. Conclusions : The findings from spectropolarimetry are complementary to those provided by optical long-baseline interferometry, allowing us to construct a coherent view of the innermost regions of a young, strongly accreting star. Yet, the strong and complex magnetic field reconstructed for S CrA N is inconsistent with the observed magnetic signatures of the emission lines associated to the post-shock region. We recommend a multi-technique, synchronized campaign of several days to put more constrains on a system that varies on a $\sim$ 1 day timescale.

Authors:Ananya Rawat, Girjesh R. Gupta

Abstract: Sunspots host various oscillations and wave phenomena like umbral flashes, umbral oscillations, running penumbral waves, and coronal waves. All fan loops rooted in sunspot umbra constantly show a 3-min period propagating slow magnetoacoustic waves in the corona. However, their origin in the lower atmosphere is still unclear. In this work, we studied these oscillations in detail along a clean fan loop system rooted in active region AR12553 for a duration of 4-hour on June 16, 2016 observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We traced foot-points of several fan loops by identifying their locations at different atmospheric heights from the corona to the photosphere. We found presence of 3-min oscillations at foot-points of all the loops and at all atmospheric heights. We further traced origin of these waves by utilising their amplitude modulation characteristics while propagating in the solar atmosphere. We found several amplitude modulation periods in the range of 9-14 min, 20-24 min, and 30-40 min of these 3-min waves at all heights. Based on our findings, we interpret that 3-min slow magnetoacoustic waves propagating in coronal fan loops are driven by 3-min oscillations observed at the photospheric foot-points of these fan loops in the umbral region. We also explored any connection between 3-min and 5-min oscillations observed at the photospheric foot-points of these loops and found them to be weakly coupled. Results provide clear evidence of magnetic coupling of the solar atmosphere through propagation of 3-min waves along fan loops at different atmospheric heights.

Authors:Daye Lim, Tom Van Doorsselaere, David Berghmans, Richard J. Morton, Vaibhav Pant, Sudip Mandal

Abstract: Transverse oscillations that do not show significant damping in solar coronal loops are found to be ubiquitous. Recently, the discovery of high-frequency transverse oscillations in small-scale loops has been accelerated by the Extreme Ultraviolet Imager onboard Solar Orbiter. We perform a meta-analysis by considering the oscillation parameters reported in the literature. Motivated by the power law of the velocity power spectrum of propagating transverse waves detected with CoMP, we consider the distribution of energy fluxes as a function of oscillation frequencies and the distribution of the number of oscillations as a function of energy fluxes and energies. These distributions are described as a power law. We propose that the power law slope ($\delta=-1.40$) of energy fluxes depending on frequencies could be used for determining whether high-frequency oscillations dominate the total heating ($\delta < 1$) or not ($\delta > 1$). In addition, we found that the oscillation number distribution depending on energy fluxes has a power law slope of $\alpha=1.00$, being less than 2, which means that oscillations with high energy fluxes provide the dominant contribution to the total heating. It is shown that, on average, higher energy fluxes are generated from higher frequency oscillations. The total energy generated by transverse oscillations ranges from about $10^{20}$ to $10^{25}$ erg, corresponding to the energies for nanoflare ($10^{24}-10^{27}$ erg), picoflare ($10^{21}-10^{24}$ erg), and femtoflare ($10^{18}-10^{21}$ erg). The respective slope results imply that high-frequency oscillations could provide the dominant contribution to total coronal heating generated by decayless transverse oscillations.

Authors:Alec Owens, Sam O. M. Wright, Yakiv Pavlenko, Alexander Mitrushchenkov, Jacek Koput, Sergei N. Yurchenko, Jonathan Tennyson

Abstract: A new molecular line list for lithium hydroxide ($^{7}$Li$^{16}$O$^{1}$H) covering wavelengths $\lambda > 1 \mu$m (the 0-10000 cm$^{-1}$ range) is presented. The OYT7 line list contains over 331 million transitions between rotation-vibration energy levels with total angular momentum up to $J=95$ and is applicable for temperatures up to $T\approx 3500$ K. Line list calculations are based on a previously published, high-level \textit{ab initio} potential energy surface and a newly computed dipole moment surface of the ground $\tilde{X}\,^1\Sigma^+$ electronic state. Lithium-containing molecules are important in a variety of stellar objects and there is potential for LiOH to be observed in the atmospheres of exoplanets. This work provides the first, comprehensive line list of LiOH and will facilitate its future molecular detection. The OYT7 line list along with the associated temperature- and pressure-dependent opacities can be downloaded from the ExoMol database at www.exomol.com and the CDS astronomical database.

Authors:Nat H. Mathews, Barbara J. Thompson

Abstract: As Physics-Informed Neural Networks and other methods for full-vector-field construction or analysis become more prominent, a need has developed for a large set of simulated active regions for training, validation and testing purposes. We use a state-of-the-art magnetohydrostatic extrapolation method to develop a public dataset of over five thousand data cubes based on the Spaceweather HMI Active Region Patch (SHARP) library of active region magnetogram images. Each cube resolves the magnetic field vector and plasma forcing at approximately 100,000 scattered points that are adaptively clustered near the high-flux regions of the domain. This paper describes the methodology of construction of the Plasma-prescribed Active Region Static Extrapolation (PARSE) dataset, as well as its structure and how to access it.

Authors:Shu Wang, Xiaodian Chen, Jianxing Zhang, Licai Deng

Abstract: RR Lyrae (RR Lyr) stars are a well-known and useful distance indicator for old stellar populations such as globular clusters and dwarf galaxies. Fundamental-mode RR Lyr (RRab) stars are commonly used to measure distances, and the accuracy of the determined distance is strongly constrained by metallicity. Here, we investigate the metallicity dependence in the period-luminosity (PL) relation of double-mode RR Lyr (RRd) stars. We find and establish a linear relation between metallicity and period or period ratio for RRd stars. This relation can predict the metallicity as accurately as the low-resolution spectra. Based on this relation, we establish a metallicity-independent PL relation for RRd stars. Combining the distance of the Large Magellanic Cloud and Gaia parallaxes, we calibrate the zero point of the derived PL relation to an error of 0.022 mag. Using RRd stars, we measure the distances of globular clusters and dwarf galaxies with an accuracy of 2-3% and 1-2%, respectively. In the future, RRd stars could anchor galaxy distances to an accuracy of 1.0% and become an independent distance ladder in the Local Group.

Authors:Andrew Hillier, Iñigo Arregui, Takeshi Matsumoto

Abstract: Magnetohydrodynamic kink waves naturally form as a consequence of perturbations to a structured medium, for example transverse oscillations of coronal loops. Linear theory has provided many insights in the evolution of linear oscillations, and results from these models are often applied to infer information about the solar corona from observed wave periods and damping times. However, simulations show that nonlinear kink waves can host the Kelvin-Helmholtz instability (KHi) which subsequently creates turbulence in the loop, dynamics which are beyond linear models. In this paper we investigate the evolution of KHi-induced turbulence on the surface of a flux tube where a non-linear fundamental kink-mode has been excited. We control our numerical experiment so that we induce the KHi without exciting resonant absorption. We find two stages in the KHi turbulence dynamics. In the first stage, we show that the classic model of a KHi turbulent layer growing $\propto t$is applicable. We adapt this model to make accurate predictions for damping of the oscillation and turbulent heating as a consequence of the KHi dynamics. In the second stage, the now dominant turbulent motions are undergoing decay. We find that the classic model of energy decay proportional to $t^{-2}$ approximately holds and provides an accurate prediction of the heating in this phase. Our results show that we can develop simple models for the turbulent evolution of a non-linear kink wave, but the damping profiles produced are distinct from those of linear theory that are commonly used to confront theory and observations.

Authors:Yael Naze ULiege, Nikolay Britavskiy ULiege, Gregor Rauw ULiege, Jonathan Labadie-Bartz Obs. Paris, S. Simon-Diaz IAC+Univ. La Laguna

Abstract: The origin of rapid rotation in massive stars remains debated, although binary interactions are now often advocated as a cause. However, the broad and shallow lines in the spectra of fast rotators make direct detection of binarity difficult. In this paper, we report on the discovery and analysis of multiplicity for three fast-rotating massive stars: HD25631 (B3V), HD191495 (B0V), and HD46485 (O7V). They display strikingly similar TESS light curves, with two narrow eclipses superimposed on a sinusoidal variation due to reflection effects. We complement these photometric data by spectroscopy from various instruments (X-Shooter, Espadons, FUSE...), to further constrain the nature of these systems. The detailed analyses of these data demonstrates that the companions of the massive OB stars have low masses (~1Msol) with rather large radii (2-4 Rsol) and low temperatures (<15 kK). These companions display no UV signature, which would exclude a hot subdwarf nature, but disentangling of the large set of X-Shooter spectra of HD25631 revealed the typical signature of chromospheric activity in the companion's spectrum. In addition, despite the short orbital periods (P=3-7d), the fast-rotating OB-stars still display non-synchronized rotation and all systems appear young (<20Myr). This suggests that, as in a few other cases, these massive stars are paired in those systems with non-degenerate, low-mass PMS companions, implying that fast rotation would not be a consequence of a past binary interactions in their case.

Authors:László Molnár, Emese Plachy, Attila Bódi, András Pál, Meridith Joyce, Csilla Kalup, Christian I. Johnson, Zoltán Dencs, Szabolcs Mészáros, Henryka Netzel, Karen Kinemuchi, Juna A. Kollmeier, Jose Luis Prieto, Aliz Derekas

Abstract: The globular cluster Messier 80 was monitored by the Kepler space telescope for 80 days during the K2 mission. Continuous, high-precision photometry of such an old, compact cluster allows us to study its variable star population in unprecedented detail. We extract light curves for 27 variable stars using differential-image photometry. A search for new variables in the images led to the discovery of two new variable stars: an RR Lyrae and a variable red giant star, respectively. Analysis of the RR Lyrae population reveals multiple RRc stars with additional modes and/or peculiar modulation cycles. We newly classify star V28 as a spotted extreme horizontal branch variable. Despite their faintness, we clearly detect the three SX Phe stars but we did not find new pulsation modes beyond the known ones in them. Spectra taken with the VLT and Magellan Clay telescopes, as well as absolute color-magnitude diagrams of the cluster based on Gaia and Pan-STARRS observations confirm the classification of the peculiar modulated variables as bona-fide RRc stars. We propose that they highlight a subgroup of overtone stars that may have been overlooked before. We fit MESA isochrones to the CMDs to estimate the age and metallicity of the cluster. We confirm that M80 is old and metal-poor, but show that isochrone fitting to old populations comes with numerous uncertainties.

Authors:D P S Nilagarathne, J Adassuriya, H O Wijewardane

Abstract: Solar flare is one of the most important solar activities which emit all electromagnetic waves in gigantic burst. The radio emission can be used to determine the physical properties of the solar flares. The e-CALLISTO worldwide network is designed to detect the radio emission of the solar flares and this study used the spectroscopic data from the e-CALLISTO system. Among the five types of solar radio bursts, this study was focused on type II radio bursts. The spectroscopic analysis estimated the shock speed of type II radio bursts using the uniform electron density model and the nonuniform electron density model of the sun. The shock speed is proportional to the electron density (Ne) and inversely proportional to the rate of change in electron density with altitude (dNe/dr). The determined shock speed at the altitude of one solar radius is 2131 km/s for uniform model and 766 km/s for non-uniform model. Although the uniform electron density model is widely used we attempted the non-uniform electron density since in the active region of the sun, the electron densities are non-uniform. The estimated shock speeds of uniform density model is relatively high so that it is reasonable to use non-uniform electron density model for shock speed estimation of type II radio bursts.

Authors:J Adassuriya, S Gunasekera, KPSC Jayaratne, C Monstein

Abstract: A CALLISTO system was set up at the Arthur C Clarke Institute and connected to the e-CALLISTO global network which observes the solar radio bursts in 24 hours. CALLISTO is the foremost observation facility to investigate celestial objects in radio region in Sri Lanka. The system consists of the CALLISTO spectrometer and controlling software,logarithmic periodic antenna and pre-amplifier. CALLISTO spectrometer is able to detect solar radio bursts in the frequency range of 45 MHz to 870 MHz with a channel resolution of 62.5 kHz.The log-periodic antenna was designed for 7 dBi gain and achieved the voltage standing wave ratio, less than 1.5 which is acquired by the overall impedance of the antenna, 49.3 ohms. The linear polarized antenna is pointing to zenith and the dipoles directed to north-south direction. The system detects solar radio emissions originated by solar flares and corona mass ejections. The radio bursts occurs as emission stripes in the radio spectra and classify from type I to V mainly on drift rate and band width. The system observed a type III solar radio burst on 5th July 2013 and a type II burst on 25th October 2013 which was originated by X1.7 solar flare. The type II bursts characterize with narrow bandwidth and drift slowly from higher to lower frequencies while the main features of type III bursts are high drift rate and broad bandwidth.

Authors:J. Gorman, L. P. Chitta, H. Peter, D. Berghmans, F. Auchère, R. Aznar Cuadrado, L. Teriaca, S. K. Solanki, C. Verbeeck, E. Kraaikamp, K. Stegen, S. Gissot

Abstract: Within the quiet Sun corona imaged at 1 MK, much of the field of view consists of diffuse emission that appears to lack the spatial structuring that is so evident in coronal loops or bright points. We seek to determine if these diffuse regions are categorically different in terms of their intensity fluctuations and spatial configuration from the more well-studied dynamic coronal features. We analyze a time series of observations from Solar Orbiter's High Resolution Imager in the Extreme Ultraviolet to quantify the characterization of the diffuse corona at high spatial and temporal resolutions. We then compare this to the dynamic features within the field of view, mainly a coronal bright point. We find that the diffuse corona lacks visible structuring, such as small embedded loops, and that this is persistent over the 25 min duration of the observation. The intensity fluctuations of the diffuse corona, which are within +/-5%, are significantly smaller in comparison to the coronal bright point. Yet, the total intensity observed in the diffuse corona is of the same order as the bright point. It seems inconsistent with our data that the diffuse corona is a composition of small loops or jets or that it is driven by discrete small heating events that follow a power-law-like distribution. We speculate that small-scale processes like MHD turbulence might be energizing the diffuse regions, but at this point we cannot offer a conclusive explanation for the nature of this feature.

Authors:M. O. Lewis, R. Bhattacharya, L. O. Sjouwerman, Y. M. Pihlström, G. Pietrzyński, R. Sahai, P. Karczmarek, M. Górski

Abstract: We establish a sample of 370 Mira variables that are likely near the Galactic center (GC). The sources have been selected from the OGLE and BAaDE surveys based on their sky coordinates, OGLE classifications, and BAaDE maser-derived line-of-sight velocities. As the distance to the GC is known to a high accuracy, this sample is a test bed for reddening and extinction studies toward the GC and in Mira envelopes. We calculated separate interstellar- and circumstellar-extinction values for individual sources, showing that there is a wide range of circumstellar extinction values (up to four magnitudes in the K$_s$ band) in the sample, and that circumstellar reddening is statistically different from interstellar reddening laws. Further, the reddening laws in the circumstellar environments of our sample and the circumstellar environments of Large Magellanic Cloud (LMC) Miras are strikingly similar despite the different metallicities of the samples. Period-magnitude relations for the mid-infrared (MIR) WISE and MSX bands are also explored, and in the WISE bands we compare these to period-magnitude relationships derived from Miras in the LMC as it is important to compare these LMC relations to those in a higher metallicity environment. Emission from the envelope itself may contaminate MIR magnitudes altering the relations, especially for sources with thick envelopes.

Authors:Andrea Ercolino, Harim Jin, Norbert Langer, Luc Dessart

Abstract: Many supernovae (SNe) imply an interaction of the SN ejecta with matter (CSM) surrounding the progenitor star. This suggests that many massive stars may undergo various degrees of envelope stripping shortly before exploding, and produce a considerable diversity in their pre-explosion CSM properties. We explore a generic set of ~100 detailed massive binary evolution models to characterize the amount of envelope stripping and the expected CSM configurations. Our binary models were computed with the MESA stellar evolution code, considering an initial primary star mass of 12.6 Msun, and focus on initial orbital periods above 500 d. We compute these models up to the time of the primary's iron core collapse. We find that Roche lobe overflow often leads to incomplete stripping of the mass donor, resulting in a large variety of pre-SN envelope masses. Many of our models' red supergiant (RSG) donors undergo core collapse during Roche lobe overflow, with mass transfer and thus system mass loss rates of up to 0.01 Msun/yr at that time. The corresponding CSM densities are similar to those inferred for Type IIn SNe like 1998S. In other cases, the mass transfer turns unstable, leading to a common envelope phase at such late time that the mass donor explodes before the common envelope is fully ejected or the system has merged. We argue that this may cause significant pre-SN variability, as for example in SN 2020tlf. Other models suggest a common envelope ejection just centuries before core collapse, which may lead to the strongest interactions, as in superluminous Type IIn SNe like 1994W, or 2006gy. Wide massive binaries offer a natural framework to understand a broad range of hydrogen-rich interacting SNe. On the other hand, the flash features observed in many Type IIP SNe, like in SN 2013fs, may indicate that RSGs are more extended than currently assumed.

Authors:Alexander J. Dimoff, Jerome A. Orosz

Abstract: Apsidal motion is the precession of the line of apsides in the orbit of a binary star due to perturbations from General Relativity (GR), tides, or third body interactions. The rate of precession due to tidal effects depends on the interior structures of the stars and, as a result, binaries where such precession occurs are of great interest. Apsidal motion is observed through the analysis of eclipse times, revealing small changes in the average interval between successive primary and secondary eclipses, taking all available observed times of eclipse and yielding an estimate of the apsidal rate. Given that this is a single observed quantity, various degeneracies are unavoidably present. Ideally, one would have a model that predicts eclipse times given the orbital and stellar parameters. These parameters for a given binary could then be computed using least squares, provided a suitably large number of eclipse times. Here we use the Eclipsing Light Curve (ELC) program as such a model. The Newtonian equations of motion with extra force terms accounting for GR contributions and tidal distortions are integrated, yielding precise sky positions as a function of time. Times of mid-eclipse and instantaneous orbital elements are computed as a function of time. In this paper we outline the method, and compare numerically computed apsidal rates with standard formulae using a set of 15 binaries based on real systems. For our simulated systems, the derived apsidal rates agree with the standard formula.

Authors:Jan Kára, Linda Schmidtobreick, Anna Francesca Pala, Claus Tappert

Abstract: Context: Several high-mass transfer cataclysmic variables show evidence for outflow from the system, which could play an important role in their evolution. We investigate the system IX Vel, which was proposed to show similar characteristics. Aims: We study the structure of the IX Vel system, particularly the structure of its accretion flow and accretion disc. Methods: We use high-resolution time-resolved spectroscopy to construct radial velocity curves of the components in IX Vel, we compute Doppler maps of the system which we use to estimate the temperature distribution maps. Results: We improve the spectroscopic ephemeris of the system and its orbital period P_orb = 0.19392793(3) d. We construct Doppler maps of the system based on hydrogen and helium emission lines and the Bowen blend. The maps show features corresponding to the irradiated face of the secondary star, the outer rim of the accretion disc, and low-velocity components located outside the accretion disc and reaching towards L3. We constructed a temperature distribution map of the system using the Doppler maps of Balmer lines. Apart from the features found in the Doppler maps, the temperature distribution map shows a region of high temperature in the accretion disc connecting the expected position of a bright spot and the inner parts of the disc. Conclusions: We interpret the low-velocity emission found in the Doppler map as emission originating in the accretion disc wind and in an outflow region located in the vicinity of the third Lagrangian point L3. This makes IX Vel a member of the RW Sex class of Cataclysmic Variables.

Authors:Jianhui Lian, Nicholas Storm, Guillaume Guiglion, Aldo Serenelli, Benoit Cote, Amanda I. Karakas, Nick Boardman, Maria Bergemann

Abstract: Most heavy elements beyond the iron peak are synthesized via neutron capture processes. The nature of the astrophysical sites of neutron capture processes is still very unclear. In this work we explore the observational constraints of the chemical abundances of s-process and r-process elements on the sites of neutron-capture processes by applying Galactic chemical evolution (GCE) models to the data from Gaia-ESO large spectroscopic stellar survey. For the r-process, the [Eu/Fe]-[Fe/H] distribution suggests a short delay time of the site that produces Eu. Other independent observations (e.g., NS-NS binaries), however, suggest a significant fraction of long delayed ($>1$Gyr) neutron star mergers (NSM). When assuming NSM as the only r-process sites, these two observational constraints are inconsistent at above 1$\sigma$ level. Including short delayed r-process sites like magneto-rotational supernova can resolve this inconsistency. For the s-process, we find a weak metallicity dependence of the [Ba/Y] ratio, which traces the s-process efficiency. Our GCE model with up-to-date yields of AGB stars qualitatively reproduces this metallicity dependence, but the model predicts a much higher [Ba/Y] ratio compared to the data. This mismatch suggests that the s-process efficiency of low mass AGB stars in the current AGB nucleosynthesis models could be overestimated.

Authors:Akash Biswas, Bidya Binay Karak, Pawan Kumar

Abstract: The prediction of the strength of an upcoming solar cycle has been a long-standing challenge in the field of solar physics. The inherent stochastic nature of the underlying solar dynamo makes the strength of the solar cycle vary in a wide range. Till now, the polar precursor methods and the dynamo simulations, that use the strength of the polar field at the cycle minimum to predict the strength of the following cycle has gained reasonable consensus by providing convergence in the predictions for solar cycles 24 and 25. Recently, it has been shown that just by using the observed correlation of the polar field rise rate with the peak of the polar field at the cycle minimum and the amplitude of the following cycle, a reliable prediction can be made much earlier than the cycle minimum. In this work, we perform surface flux transport (SFT) simulations to explore the robustness of this correlation against the stochastic fluctuations of BMR tilt properties including anti-Joy and anti-Hale type anomalous BMRs, and against the variation of meridional flow speed. We find that the observed correlation is a robust feature of the solar cycles and thus it can be utilized for a reliable prediction of solar cycle much earlier than the cycle minimum, the usual landmark of the solar cycle prediction.

Authors:Bao Truong, Thiem Hoang, Nguyen Chau Giang, Pham Ngoc Diep, Dieu D. Nguyen, Nguyen Bich Ngoc

Abstract: Magnetic fields are thought to influence the formation and evolution of evolved star envelopes. Thermal dust polarization from magnetically aligned grains is potentially a powerful tool for probing magnetic fields and dust properties in these circumstellar environments. In this paper, we present numerical modeling of thermal dust polarization from the envelope of IK Tau using the magnetically enhanced radiative torque (MRAT) alignment theory implemented in our updated POLARIS code. Due to the strong stellar radiation field, the minimum size required for RAT alignment of silicate grains is $\sim 0.005 - 0.05\,\rm\mu m$. Additionally, ordinary paramagnetic grains can achieve perfect alignment by MRAT in the inner regions of $r < 500\,\rm au$ due to stronger magnetic fields of $B\sim 10$ mG - 1G, producing thermal dust polarization degree of $\sim 10\,\%$. The polarization degree can be enhanced to $\sim 20-40\%$ for grains with embedded iron inclusions. We also find that the magnetic field geometry affects the alignment size and the resulting polarization degree due to the projection effect in the plane-of-sky. We also study the spectrum of polarized thermal dust emission and find the increased polarization degree toward $\lambda > 50\,\rm\mu m$ due to the alignment of small grains by MRAT. Furthermore, we investigate the impact of rotational disruption by RATs (RAT-D) and find the RAT-D effect cause a decrease in the dust polarization fraction. Finally, we compare our numerical results with available polarization data observed by SOFIA/HAWC+ for constraining dust properties, suggesting grains are unlikely to have embedded iron clusters and might have slightly elongated shapes. Our modeling results suggest further observational studies at far-infrared/sub-millimeter wavelengths to understand the properties of magnetic fields and dust in AGB envelopes.

Authors:V. V. Dorovskyy, V. N. Melnik, A. A. Konovalenko, A. I. Brazhenko, H. O. Rucker

Abstract: We present the results of observations of complex powerful type II burst associated with narrow Earth-directed CME, which was ejected at around 11 UT on 31 May 2013. The observations were performed by radio telescope UTR-2, which operated as local interferometer, providing the possibility of detection of the spatial parameters of the radio emission source. There are also polarization data from URAN-2 radio telescope. The CME was detected by two space-born coronagraphs SOHO/LASCO/C2 and STEREO/COR1-BEHIND, and was absolutely invisible for STEREO-AHEAD spacecraft. The associated type II burst consisted of two successive parts of quite different appearance on the dynamic spectrum. The first burst was narrow in frequency, had cloudy structure and was completely unpolarized while the second one represented rich herring-bone structure and exposed high degree of circular polarization. Both parts of the whole event reveal band splitting and well distinguished harmonic structure. The positions and sizes of the sources of the type II burst were found using cross-correlation functions of interferometer bases. The sources of the type II bursts elements were found to be of about 15 arcmin in size in average, with the smallest ones reaching as low as 10 arcmin. Corresponding brightness temperatures were estimated. In most cases these temperatures were between $10^{11}$ and $10^{12}$ K with maximum value as high as $10^{14}$ K. The spatial displacement of the source was measured and model independent velocities of the type II burst sources were determined.

Authors:Anju Panthi, Annapurni Subramaniam, Kaushar Vaidya, Vikrant Jadhav, Sharmila Rani, Sivarani Thirupathi, Sindhu Pandey, Snehalata Sahu

Abstract: Blue metal-poor stars are main-sequence stars that are bluer and brighter than typical turn-off stars in metal-poor globular clusters. They are thought to have either evolved through post-mass transfer mechanisms as field blue straggler stars or have accreted from Milky Way dwarf satellite galaxies. It has been found that a considerable fraction of blue metal poor stars are binaries, possibly with a compact companion. We observed 27 blue metal poor stars using UV imaging telescope of AstroSat in two far-UV filters, F148W and F169M. In this work, we explain the possible formation channels of two stars, BMP17 and BMP37. We fit BMP17 with a single-component spectral energy distribution whereas BMP37 with a binary-component spectral energy distribution. As both of them are known SB1s, we suggest that the WD companion of BMP17 may have cooled down so that it is out of UV imaging telescope detection limit. On the other hand, we discover a normal mass white dwarf as the hot companion of BMP37, indicating mass transfer as the possible formation channel

Authors:Masahito Kubo, Yukio Katsukawa, David Hernández Expósito, Antonio Sánchez Gómez, María Balaguer Jimenéz, David Orozco Suárez, José M. Morales Fernández, Beatriz Aparicio del Moral, Antonio J. Moreno Mantas, Eduardo Bailón Martínez, Jose Carlos del Toro Iniesta, Yusuke Kawabata, Carlos Quintero Noda, Takayoshi Oba, Ryohtaroh T. Ishikawa, Toshifumi Shimizu

Abstract: The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) has been developed for the third flight of the SUNRISE balloon-borne stratospheric solar observatory. The aim of SCIP is to reveal the evolution of three-dimensional magnetic fields in the solar photosphere and chromosphere using spectropolarimetric measurements with a polarimetric precision of 0.03\% (1$\sigma$). Multiple lines in the 770 and 850 nm wavelength bands are simultaneously observed with two 2k$\times$2k CMOS cameras at a frame rate of 31.25 Hz. Stokes profiles are calculated onboard by accumulating the images modulated by a polarization modulation unit, and then compression processes are applied to the two-dimensional maps of the Stokes profiles. This onboard data processing effectively reduces the data rate. SCIP electronics can handle large data formats at high speed. Before the implementation into the flight SCIP electronics, a performance verification of the onboard data processing was performed with synthetic SCIP data that were produced with a numerical simulation modeling the solar atmospheres. Finally, we verified that the high-speed onboard data processing was realized on ground with the flight hardware by using images illuminated by natural sunlight or an LED.

Authors:M. Nelissen, A. Natta, P. McGinnis, C. Pittman, C. Delvaux, T. Ray

Abstract: Classical T Tauri stars (cTTs) accrete from their circumstellar disk. The material falls onto the stellar surface, producing an accretion shock, which generates veiling in a star's spectra. In addition, the shock causes a localized accretion spot at the level of the chromosphere. Our goal is to investigate the accretion, particularly the mass accretion rates (Macc), for the cTTs DK Tau, over two periods of 17 and 29 days, using two different procedures for comparison purposes. The first method relies on the derivation of the accretion luminosity via accretion-powered emission lines. The second compares the variability of the optical veiling with accretion shock models to determine mass accretion rates. We used observations taken in 2010 and 2012 with the ESPaDOnS spectropolarimeter at the CFHT. We find peak values of the veiling (at 550 nm) ranging from 0.2 to 1.3, with a steeper trend across the wavelength range for higher peak values. When using the accretion-powered emission lines, we find mass accretion rate values ranging from log(Macc[Msol/yr]) = -8.20 to log(Macc[Msol/yr]) = -7.40. This agrees with the values found in the literature, as well as the values calculated using the accretion shock models and the veiling. In addition, we identify a power-law correlation between the values of the accretion luminosity and the optical veiling. For the 2010 observations, using the values of the filling factors (which represent the area of the star covered by an accretion spot) derived from the shock models, we infer that the accretion spot was located between +45 degrees and +75 degrees in latitude. We show that both methods of determining the mass accretion rate yield similar results. We also present a helpful means of confirming the accretion luminosity values by measuring the veiling at a single wavelength in the optical.

Authors:Kateryna Andrych, Devika Kamath, Jacques Kluska, Hans Van Winckel, Steve Ertel, Akke Corporaal

Abstract: Binary post-asymptotic giant branch (post-AGB) stars are products of a poorly understood binary interaction process that occurs during the AGB phase. These systems comprise of a post-AGB primary star, a main-sequence secondary companion and a stable circumbinary disc. Studying the structure and properties of these circumbinary discs is crucial for gaining insight into the binary interaction process that governs post-AGB binaries as well as comprehending the disc's creation, evolution, and its interaction with the post-AGB binary system. We aim to use near-infrared polarimetric imaging to investigate the morphology and potential substructures of circumbinary discs around eight representative post-AGB binary stars. To achieve this, we performed polarimetric differential imaging in H and Y bands using the high-angular resolution capabilities of the European Southern Observatory-Very Large Telescope/SPHERE-Infra-Red Dual-beam Imaging and Spectroscopy instrument. We resolved the extended circumbinary disc structure for a diverse sample of eight post-AGB binary systems. Our analysis provided the first estimates of the disc scale-height for two of the systems: IW Car and IRAS 15469-5311. We also investigated the morphological differences between the full discs (with the inner rim at the dust sublimation radius) and transition discs (which are expected to have larger inner cavities), as well as similarities to protoplanetary disks around young stellar objects. We found that the transition discs displayed a more intricate and asymmetric configuration. Surprisingly, no correlation was found between the over-resolved flux in near-IR interferometric data and the polarimetric observations, suggesting that scattering of light on the disc surface may not be the primary cause of the observed over-resolved flux component.

Authors:S. Chevalier, C. Babusiaux, T. Merle, F. Arenou

Abstract: The recent Gaia third data release (DR3) has brought some new exciting data about stellar binaries. It provides new opportunities to fully characterize more stellar systems and contribute to enforce our global knowledge of stars behaviour. By combining the new Gaia non-single stars catalog with double-lined spectroscopic binaries (SB2), one can determine the individual masses and luminosities of the components. To fit an empirical mass-luminosity relation in the Gaia G band, lower mass stars need to be added. Those can be derived using Gaia resolved wide binaries combined with literature data. Using the BINARYS tool, we combine the astrometric non-single star solutions in the Gaia DR3 with SB2 data from two other catalogs : the 9th Catalogue of Spectroscopic Binary orbits (SB9) and APOGEE. We also look for low mass stars resolved in Gaia with direct imaging and Hipparcos data or literature mass fraction. The combination of Gaia astrometric non-single star solutions with double-lined spectroscopic data enabled to characterize 43 binary systems with SB9 and 13 with APOGEE. We further derive the masses of 6 low mass binaries resolved with Gaia. We then derive an empirical mass-luminosity relation in the Gaia G band down to 0.12 Msun.

Authors:O. V. Kiyaeva The Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, I. S. Izmailov The Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, N. V. Narizhnaya The Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, L. G. Romanenko The Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo

Abstract: Star ADS 9173=WDS 14135+5147=Hip 69483 is a complex system. The B component has a spectroscopic companion, whose orbit with a period of 4.9 years has been known since 1986. The Gaia telescope has detected a distant faint pair over 100 arcsec away from the bright AB pair. In our article, we study the movement in a bright pair based on long-term observations with the 26-inch refractor of the Pulkovo Observatory. The AB pair orbit with a period of 6306 years was calculated using the apparent motion parameters (AMP) method. The astrometric orbit of the component B was determined on the basis of the residuals of the homogeneous CCD observations up to 2023 with the 26-inch refractor. It is in agreement with the spectroscopic one. The remaining secondary residuals show a wave with a period of approximately 20 years, the reasons for which are discussed.

Authors:Zahra Tajik, Nastaran Frahang, Hossein Safari, Michael S. Wheatland

Abstract: Solar and stellar magnetic patches (i.e., magnetic fluxes that reach the surface from the interior) are believed to be the primary sources of a star's atmospheric conditions. Hence, detecting and identifying these features (also known as magnetic elements) are among the essential topics in the community. Here, we apply the complex network approach to recognize the solar magnetic patches. For this purpose, we use the line-of-sight magnetograms provided by the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory. We construct the magnetic network following a specific visibility graph condition between pairs of pixels with opposite polarities and search for possible links between these regions. The complex network approach also provides the ability to rank the patches based on their connectivity (i.e., degree of nodes) and importance (i.e., PageRank). The use of the developed algorithm in the identification of magnetic patches is examined by tracking the features in consecutive frames, as well as making a comparison with the other approaches to identification. We find that this method could conveniently identify features regardless of their sizes. For small-scale (one or two pixels) features, we estimate the average of 8% false-positive and 1% false-negative errors.

Authors:Laura Lenkić, Conor Nally, Olivia C. Jones, Martha L. Boyer, Patrick J. Kavanagh, Nolan Habel, Omnayarani Nayak, Alec S. Hirschauer, Margaret Meixner, B. A. Sargent, Tea Temim

Abstract: We present an imaging survey of the Spitzer~I star-forming region in NGC 6822 conducted with the NIRCam and MIRI instruments onboard JWST. Located at a distance of 490 kpc, NGC 6822 is the nearest non-interacting low-metallicity ($\sim$0.2 $Z_{\odot}$) dwarf galaxy. It hosts some of the brightest known HII regions in the local universe, including recently discovered sites of highly-embedded active star formation. Of these, Spitzer I is the youngest and most active, and houses 90 color-selected candidate young stellar objects (YSOs) identified from Spitzer Space Telescope observations. We revisit the YSO population of Spitzer~I with these new JWST observations. By analyzing color-magnitude diagrams (CMDs) constructed with NIRCam and MIRI data, we establish color selection criteria and construct spectral energy distributions (SEDs) to identify candidate YSOs and characterize the full population of young stars, from the most embedded phase to the more evolved stages. In this way, we have identified 129 YSOs in Spitzer I. Comparing to previous Spitzer studies of the NGC 6822 YSO population, we find that the YSOs we identify are fainter and less massive, indicating that the improved resolution of JWST allows us to resolve previously blended sources into individual stars.

Authors:M. Correa, J. M. Vilalta, J. F. Le Borgne

Abstract: During a screening in ASAS-SN database searching candidates of Delta Scuti stars with short period, our attention was drawn to the variable star ASASSN-V J104912.47+274312.7, we considered interesting to follow. It is an ASAS-SN discovery, classified by them as a RRc. We observed it for 16 nights in 2021, obtaining several maxima that allow us to refine its period. After a frequency analysis, we conclude that this star belongs to a small subgroup of RRc stars having the peculiarity to show two close frequencies with ratio greater than 0.96, without 0.61 or 0.68 period ratio mode. This behaviour is very similar to two stars found by Netzel & Smolec (2019) in OGLE data, and one star in NGC 6362, studied by Smolec et al. (2017). This large period ratios are also found as additional mode to standard double mode RRc stars (Px/Pl= 0.61-0.68) by Netzel et al. (2023).

Authors:D. Wang, B. P. Gong

Abstract: The millisecond pulsar(MSP) is believed to be an old neutron star(NS) having undergone spin-up by the accreting material from the donor. Whereas, the discovery of eccentric millisecond pulsars (eMSPs) in the Galactic field challenges such a scenario producing MSP-white dwarf (WD) only in the circular orbit. As orbital periods and companion mass of these eMSPs are located in a narrow range, a reasonable postulation is that they have the same origin. Although many models have been proposed to interpret their origin, however, the origin of the narrow range of the orbital period is still an open question. The accretion-induced collapse(AIC) of the ONe WD is considered to be an important pathway to form MSP, which was expected to result in the formation of MSP in the circular orbit due to tidal circularization. Here we revisited this scenario by the binary population synthesis including the specific circularization calculation. Our results indicate that binaries with insufficient circularization in this scenario can evolve into the eMSPs. The narrow initial binary parameters required by insufficient circularization can naturally account for the narrow range of the orbital period. Although the evolution of WD's AIC process has not been well understood, the characteristic of a narrow range in the orbital period of eMSPs can still set constraints on the physics of their evolution.

Authors:Vito Tuhtan, Rami Al-Belmpeisi, Mikkel Bregning Christensen, Rajika L Kuruwita, Troels Haugbølle

Abstract: Protostellar binaries harbour complex environment morphologies. Observations represent a snapshot in time, and projection and optical depth effects impair our ability to interpret them. Careful comparison with high-resolution models that include the larger star-forming region can help isolate the driving physical processes and give observations context in the time domain. We carry out zoom-in simulations with AU-scale resolution, and for the first time ever we follow the evolution until a circumbinary disk is formed. We investigate the gas dynamics around the young stars and extract disk sizes. Using radiative transfer, we obtain evolutionary tracers of the binary systems. We find that the centrifugal radius in prestellar cores is a poor estimator of the resulting disk size due to angular momentum transport at all scales. For binaries, the disk sizes are regulated periodically by the binary orbit, having larger radii close to the apastron. The bolometric temperature differs systematically between edge-on and face-on views and shows a high frequency time dependence correlated with the binary orbit and a low frequency time dependence with larger episodic accretion events. These oscillations can bring the system appearance to change rapidly from class 0 to class I and for short time periods even bring it to class II. The highly complex structure in early stages, as well as the binary orbit itself, affects the classical interpretation of protostellar classes and direct translation to evolutionary stages has to be done with caution and include other evolutionary indicators such as the extent of envelope material.

Authors:Valeriia Liakh, Rony Keppens

Abstract: We present a 2.5-dimensional magnetohydrodynamic simulation of a systematically rotating prominence inside its coronal cavity using the open-source \texttt{MPI-AMRVAC} code. Our simulation starts from a non-adiabatic, gravitationally stratified corona, permeated with a sheared arcade magnetic structure. The flux rope (FR) is formed through converging and shearing footpoints driving, simultaneously applying randomized heating at the bottom. The latter induces a left-right asymmetry of temperature and density distributions with respect to the polarity-inversion line. This asymmetry drives flows along the loops before the FR formation, which gets converted to net rotational motions upon reconnection of the field lines. As the thermal instability within the FR develops, angular momentum conservation about its axis leads to a systematic rotation of both hot coronal and cold condensed plasma. The initial rotational velocity exceeds $60\ \mathrm{km\ s^{-1}}$. The synthesized images confirm the simultaneous rotations of the coronal plasma seen in 211 and 193 \AA\ and condensations seen in 304 \AA. Furthermore, the formation of the dark cavity is evident in 211 and 193 \AA\ images. Our numerical experiment is inspired by observations of so-called giant solar prominence tornadoes, and reveals that asymmetric FR formation can be crucial in triggering rotational motions. We reproduce observed spinning motions inside the coronal cavity, augmenting our understanding of the complex dynamics of rotating prominences.

Authors:Sirina Prasad, Qizhou Zhang, James Moran, Yue Cao, Izaskun Jimenéz-Serra, Jesus Martín-Pintado, Antonio Martinez Henares, Alejandro Báez Rubio

Abstract: MWC 349A is one of the rare stars known to have hydrogen radio recombination line (RRL) masers. The bright maser emission makes it possible to study the dynamics of the system at milli-arcsecond (mas) precision. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 1.4 mm and 0.8 mm continuum emission of MWC 349A, as well as the H30$\alpha$ and H26$\alpha$ RRLs. Using the most extended array configuration of C43-10 with a maximum baseline of 16.2km, we spatially resolved the H30$\alpha$ line and 1.4mm continuum emission for the first time. In addition to the known H30$\alpha$ and H26$\alpha$ maser emission from a Keplerian disk at LSR velocities from -12 to 28 km s$^{-1}$ and from an ionized wind for velocities between -12 to -40 km s$^{-1}$ and 28 to 60 km s$^{-1}$, we found evidence of a jet along the polar axis at $V_{\mathrm{LSR}}$ from -85 to -40 km s$^{-1}$ and +60 to +100 km s$^{-1}$. These masers are found in a linear structure nearly aligned with the polar axis of the disk. If these masers lie close to the polar axis, their velocities could be as high as 575 km s$^{-1}$, which cannot be explained solely by a single expanding wind as proposed in B\'aez Rubio et al (2013). We suggest that they originate from a high-velocity jet, likely launched by a magnetohydrodynamic wind. The jet appears to rotate in the same direction as the rotation of the disk. A detailed radiative transfer modeling of these emissions will further elucidate the origin of these masers in the wind.

Authors:Nikoleta Ilić, Katja Poppenhaeger, Desmond Dsouza, Scott J. Wolk, Marcel A. Agüeros, Beate Stelzer

Abstract: The magnetic activity of low-mass stars changes as they age. The primary process decreasing the stellar activity level is the angular momentum loss via magnetized stellar wind. However, processes like tidal interactions between stars and their close companions may slow down the braking effect and the subsequent decrease of the activity level. Until now, the tidal impact of substellar objects like brown dwarfs on the evolution of their central stars has not been quantified. Here, we analyse the X-ray properties of NLTT 41135, an M dwarf tightly orbited by a brown dwarf, to determine the impact of tidal interactions between them. We find that NLTT 41135 is more than an order of magnitude brighter in the X-ray regime than its stellar companion NLTT 41136, also an M dwarf star, with whom it forms a wide binary system. To characterize the typical intrinsic activity scatter between coeval M dwarf stars, we analyse a control sample of 25 M dwarf wide binary systems, observed with XMM-Newton and Chandra telescopes and the eROSITA instrument onboard the Spectrum R\"ontgen Gamma satellite. The activity difference in the NLTT 41135/41136 system is a $3.44 \sigma$ outlier compared to the intrinsic activity scatter of the control systems. Therefore, the most convincing explanation for the observed activity discrepancy is tidal interactions between the M dwarf and its brown dwarf. This shows that tidal interactions between a star and a substellar companion can moderately alter the expected angular-momentum evolution of the star, making standard observational proxies for its age, such as X-ray emission, unreliable.

Authors:A. Frasca, J. Alonso-Santiago, G. Catanzaro, A. Bragaglia, V. D'Orazi, X. Fu, A. Vallenari, G. Andreuzzi

Abstract: We report the discovery of a low-mass totally eclipsing system in the young (age$\simeq$28 Myr) open cluster NGC2232, during a scrutiny of their TESS light curves. The follow-up study of this detached system, TIC 43152097, is based on photometry and high-resolution spectra from the literature and purposely collected. The radial velocity of the center of mass, as well as the photospheric lithium abundance of the binary components, confirm its membership to NGC2232. By analyzing the existing photometric and spectroscopic data, we obtain orbital elements and fundamental stellar parameters for the two stars. The primary component of TIC 43152097 is a late F-type dwarf (Teff = 6070 K), while the lower-mass secondary results to be a late K-type star (Teff = 4130 K) that is still in the pre-main-sequence phase. The precise measurements of radii, masses, and effective temperatures, enabled by the simultaneous solution of light and radial velocity curves, indicate radius inflation for the K-type component, which turns out to be 7-11 % larger than predicted by standard evolutionary models. More sophisticated models incorporating both inhibition of convective energy transport caused by sub-photospheric magnetic fields and the effects by cool starspots covering a substantial fraction of the stellar surface (30-60 %) allow reproducing the position of the secondary component in the Hertzsprung-Russell and Mass-Radius diagrams.

Authors:Aleks Scholz St Andrews, Koraljka Muzic Lisbon, Porto, Victor Almendros-Abad Lisbon, Antonella Natta Dublin, Dary Ruiz-Rodriguez NRAO, Lucas Cieza Santiago, Cristina Rodriguez-Lopez Granada

Abstract: We report on a search for variability in the young brown dwarf SST1624 (~M7 spectral type, M~0.05Msol), previously found to feature an expanding gaseous shell and to undergo quasi-spherical mass loss. We find no variability on timescales of 1-6hours. Specifically, on these timescales, we rule out the presence of a period with amplitude >1%. A photometric period in that range would have been evidence for either pulsation powered by Deuterium burning or rotation near breakup. However, we see a 3% decrease in the K-band magnitude between two consecutive observing nights (a 10sigma result). There is also clear evidence for variations in the WISE lightcurves at 3.6 and 4.5 microns on timescales of days, with a tentative period of 6d, and potentially long-term variations over time windows of years. The best explanation for the variations over days is rotational modulation due to spots. These results disfavour centrifugal winds driven by fast rotation as mechanism for the mass loss, which, in turn, makes the alternative scenario -- a thermal pulse due to Deuterium burning -- more plausible.

Authors:S. Gissot, F. Auchère, D. Berghmans, B. Giordanengo, A. BenMoussa, J. Rebellato, L. Harra, D. Long, P. Rochus, U. Schühle, R. Aznar Cuadrado, F. Delmotte, C. Dumesnil, A. Gottwald, J. -P. Halain, K. Heerlein, M. -L. Hellin, A. Hermans, L. Jacques, E. Kraaikamp, R. Mercier, P. Rochus, P. J. Smith, L. Teriaca, C. Verbeeck

Abstract: The $\textrm{HRI}_\textrm{EUV}$ telescope was calibrated on ground at the Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, using the Metrology Light Source (MLS) synchrotron in April 2017 during the calibration campaign of the Extreme Ultraviolet Imager (EUI) instrument onboard the Solar Orbiter mission. We use the pre-flight end-to-end calibration and component-level (mirror multilayer coatings, filters, detector) characterization results to establish the beginning-of-life performance of the $\textrm{HRI}_\textrm{EUV}$ telescope which shall serve as a reference for radiometric analysis and monitoring of the telescope in-flight degradation. Calibration activities at component level and end-to-end calibration of the instrument were performed at PTB/MLS synchrotron light source (Berlin, Germany) and the SOLEIL synchrotron. Each component optical property is measured and compared to its semi-empirical model. This pre-flight characterization is used to estimate the parameters of the semi-empirical models. The end-to-end response is measured and validated by comparison with calibration measurements, as well as with its main design performance requirements. The telescope spectral response semi-empirical model is validated by the pre-flight end-to-end ground calibration of the instrument. It is found that $\textrm{HRI}_\textrm{EUV}$ is a highly efficient solar EUV telescope with a peak efficiency superior to 1 e$^-$.ph$^{-1}$), low detector noise ($\approx$ 3 e- rms), low dark current at operating temperature, and a pixel saturation above 120 ke- in low-gain or combined image mode. The ground calibration also confirms a well-modeled spectral selectivity and rejection, and low stray light. The EUI instrument achieves state-of-the-art performance in terms of signal-to-noise and image spatial resolution.

Authors:J. -F. Donati, L. T. Lehmann, P. I. Cristofari, P. Fouqué, C. Moutou, P. Charpentier, M. Ould-Elhkim, A. Carmona, X. Delfosse, E. Artigau, S. H. P. Alencar, C. Cadieux, L. Arnold, P. Petit, J. Morin, T. Forveille, R. Cloutier, R. Doyon, G. Hébrard, the SLS collaboration

Abstract: We present near-infrared spectropolarimetric observations of a sample of 43 weakly- to moderately-active M dwarfs, carried with SPIRou at the Canada-France-Hawaii Telescope in the framework of the SPIRou Legacy Survey from early 2019 to mid 2022. We use the 6700 circularly polarised spectra collected for this sample to investigate the longitudinal magnetic field and its temporal variations for all sample stars, from which we diagnose, through quasi-periodic Gaussian process regression, the periodic modulation and longer-term fluctuations of the longitudinal field. We detect the large-scale field for 40 of our 43 sample stars, and infer a reliable or tentative rotation period for 38 of them, using a Bayesian framework to diagnose the confidence level at which each rotation period is detected. We find rotation periods ranging from 14 to over 60d for the early-M dwarfs, and from 70 to 200d for most mid- and late-M dwarfs (potentially up to 430d for one of them). We also find that the strength of the detected large-scale fields does not decrease with increasing period or Rossby number for the slowly rotating dwarfs of our sample as it does for higher-mass, more active stars, suggesting that these magnetic fields may be generated through a different dynamo regime than those of more rapidly rotating stars. We also show that the large-scale fields of most sample stars evolve on long timescales, with some of them globally switching sign as stars progress on their putative magnetic cycles.

Authors:Simon Blouin, Mukremin Kilic, Antoine Bédard, Pier-Emmanuel Tremblay

Abstract: The convective dredge-up of carbon from the interiors of hydrogen-deficient white dwarfs has long been invoked to explain the presence of carbon absorption features in the spectra of cool DQ stars ($T_{\rm eff} < 10{,}000\,{\rm K}$). It has been hypothesized that this transport process is not limited to DQ white dwarfs and also operates, albeit less efficiently, in non-DQ hydrogen-deficient white dwarfs within the same temperature range. This non-DQ population is predominantly composed of DC white dwarfs, which exhibit featureless optical spectra. However, no direct observational evidence of ubiquitous carbon pollution in DC stars has thus far been uncovered. In this Letter, we analyze data from the Galaxy Evolution Explorer (GALEX) to reveal the photometric signature of ultraviolet carbon lines in most DC white dwarfs in the $8500\,{\rm K} \leq T_{\rm eff} \leq 10{,}500\,{\rm K}$ temperature range. Our results show that the vast majority of hydrogen-deficient white dwarfs experience carbon dredge-up at some point in their evolution.

Authors:Hamid Saleem, Zain H. Saleem

Abstract: Physical mechanism for the creation of solar spicules with three stages of their life cycle is investigated. It is assumed that at stage-I, the density hump is formed locally in the chromosphere in the presence of temperature gradients of electrons and ions along the z-axis. The density structure is accelerated in the vertical direction due to the thermal force ${\bf F}_{th} \propto \nabla n(x,y,t) \times (\nabla T_e + \nabla T_i)$. The magnitude of the upward acceleration depends on the steepness of the temperature gradients $\nabla T_j$ where $j=(e,i)$. The exact time-dependent 2D analytical solution of two fluid plasma equations is presented assuming that the exponentially decaying density structure is created in the xy plane and evolves in time as a step function $H(t)$ . The upward acceleration $a$ produced in this density structure is greater than the downward solar acceleration $g_\odot$. The vertical plasma velocity turns out to be the ramp function of time $R(t)$ whereas the source term for the density follows the delta function $\delta(t)$. In the transition region (TR), the temperature gradients are steeper and itupward acceleration increases in magnitude $g_\odot << a$ and density hump spends lesser time here. This is stage-II of its life cycle. In stage-III, the density structure enters the corona where the gradients of temperatures vanish and structure moves upward with almost constant speed which is slowly reduced to zero due to negative solar gravitational force because ${\bf a} \simeq - {\bf g}_\odot$. The estimates of height $H$ and life time $\tau_l$ of the spicule are in agreement with the observed values.

Authors:Yael Naze FNRS/ULiege, Jan Robrade Hamburger Sternwarte

Abstract: Massive stars are known X-ray emitters and those belonging to the Be category are no exception. One type of X-ray emission even appears specific to that category, the gamma Cas phenomenon. Its actual incidence has been particularly difficult to assess. Thanks to four semesters of sky survey data taken by SRG (Spectrum Roentgen Gamma)/eROSITA, we revisit the question of the X-ray properties of Be stars. Amongst a large catalog of Be stars, eROSITA achieved 170 detections (20% of sample), mostly corresponding to the earliest spectral types and/or close objects. While X-ray luminosities show an uninterrupted increasing trend with the X-ray-to-bolometric luminosity ratios, the X-ray hardness was split between a large group of soft (and fainter on average) sources and a smaller group of hard (and brighter on average) sources. The latter category gathers at least 34 sources, nearly all displaying early spectral types. Only a third of them were known before to display such X-ray properties. The actual incidence of hard and bright X-rays amongst early-type Be stars within 100--1000pc appears to be ~12%, which is far from negligible. At the other extreme, no bright supersoft X-ray emission seem to be associated to any of our targets.

Authors:F. Malara, S. Perri, J. Giacalone, G. Zimbardo

Abstract: Context. Recent spacecraft observations in the inner heliosphere have revealed the presence of local Alfvenic reversals of the magnetic field, while the field magnitude remains almost constant. They are called magnetic switchbacks and are very common in the plasma environment close to the Sun explored by the Parker Solar Probe satellite. Aims. A simple numerical model of a magnetic field reversal with constant magnitude is used in order to explore the influence of switchbacks on the propagation of energetic particles, within a range of energy typical of solar energetic particles. Methods. We model the reversal as a region of space of adjustable size bounded by two rotational discontinuities. By means of test particle simulations, beams of mono-energetic particles can be injected upstream of the switchback with various initial pitch- and gyro-phase angles. In each simulation, the particle energy may also be changed. Results. Particle dynamics is highly affected by the ratio between the particle gyroradius and the size of the switchback, with multiple pitch-angle scatterings when the particle gyroradius is of the order of the switchback size. Further, particle motion is extremely sensitive to the initial conditions implying a transition to chaos; for some parameters of the system, a large share of particles is reflected backwards upstream as they interact with the switchback. These results can have a profound impact on the solar energetic particle transport in the inner heliosphere, thus possible comparisons with in-situ spacecraft data are discussed.

Authors:Leon Ofman, Scott A Boardsen, Lan K Jian, Parisa Mostafavi, Jaye L Verniero, Roberto Livi, Michael McManus, Ali Rahmati, Davin Larson, Michael L Stevens

Abstract: Past observations show that solar wind (SW) acceleration occurs inside the sub-Alfvenic region, reaching the local Alfven speed at typical distances ~ 10 - 20 Rs (solar radii). Recently, Parker Solar Probe (PSP) traversed regions of sub-Alfvenic SW near perihelia in encounters E8-E12 for the first time providing data in these regions. It became evident that properties of the magnetically dominated SW are considerably different from the super-Alfvenic wind. For example, there are changes in relative abundances and drift of alpha particles with respect to protons, as well as in the magnitude of magnetic fluctuations. We use data of the magnetic field from the FIELDS instrument, and construct ion velocity distribution functions (VDFs) from the sub-Alfvenic regions using Solar Probe Analyzer Ions (SPAN-I) data, and run 2.5D and 3D hybrid models of proton-alpha sub-Alfvenic SW plasma. We investigate the nonlinear evolution of the ion kinetic instabilities in several case studies, and quantify the transfer of energy between the protons, alpha particles, and the kinetic waves. The models provide the 3D ion VDFs at the various stages of the instability evolution in the SW frame. By combining observational analysis with the modeling results, we gain insights on the evolution of the ion instabilities, the heating and the acceleration processes of the sub-Alfvenic SW plasma and quantify the exchange of energy between the magnetic and kinetic components. The modeling results suggest that the ion kinetic instabilities are produced locally in the SW, resulting in anisotropic heating of the ions, as observed by PSP.

Authors:Elena M. Golubeva, Akash Biswas, Anna I. Khlystova, Pawan Kumar, Bidya Binay Karak

Abstract: The polar field reversal is a crucial process in the cyclic evolution of the large-scale magnetic field of the Sun.Various important characteristics of a solar cycle, such as its duration and strength, and also the cycle predictability, are determined by the polar field reversal time. While the regular measurements of solar magnetic field have been accumulated for more than half a century, there is no consensus in the heliophysics community concerning the interpretation of the Sun's polar field measurements and especially the determination of polar field reversal time. There exists a severe problem of non-reproducibility in the reported results even from studies of the same observational dataset, and this causes an obstacle to make more accurate forecasts of solar cycle. Here, we analyze the solar magnetograms from four instruments for the last four cycles, to provide a more correct interpretation of the polar field observations and to find more accurate time of the reversals. We show the absence of triple (multipolar) reversals in Cycles 21 - 24, significant variations in the time interval between reversals in the hemispheres and in the time interval between a reversal and a cycle beginning. In order to understand the origin of the reversal time variation, we perform Surface Flux Transport (SFT) simulations and find out that the presence of the 'anomalous' bipolar magnetic regions (BMRs) in different phases of a cycle can cause cycle-to-cycle variations of the reversal time within the similar range found in observations.

Authors:Tinne Pauwels, Maddalena Reggiani, Hugues Sana, Alan Rainot, Kaitlin Kratter

Abstract: One of the most remarkable properties of massive stars is that almost all of them are found in binaries or higher-order multiple systems. Observations that cover the full companion mass ratio and separation regime are essential to constrain massive star and binary formation theories. We used VLT/SPHERE to characterise the multiplicity properties of 20 OB stars in the active star-forming region Sco OB1. We simultaneously observed with the IFS and IRDIS instruments, obtaining high-contrast imaging observations that cover a field of view of 1".73 x 1".73 in YJH bands and 11" x 12".5 in $K_1$ and $K_2$ bands, respectively, corresponding to a separation range between $\sim$200 and 9000 AU. The observations reach contrast magnitudes down to $\Delta K_1 \sim 13$, allowing us to detect companions at the stellar-substellar boundary. In total, we detect 789 sources, most of which are likely background or foreground objects. We obtain SPHERE companion fractions of $2.3 \pm 0.4$ and $4.2 \pm 0.8$ for O- and B-type stars, respectively. Including all previously detected companions, we find a total multiplicity fraction of $0.89\pm0.07$ for our sample in the range of $\sim$0-12000 AU. In conclusion, SPHERE explores an as of yet uncharted territory of companions around massive stars, which is crucial to ultimately improve our understanding of massive star and binary formation.

Authors:Ali Pourmand, Natalia Ivanova

Abstract: Evolutionary calculations for stars in close binary systems are in high demand to obtain better constraints on gravitational wave source progenitors, understand transient events from stellar interactions, and more. Modern one-dimensional stellar codes make use of the Roche lobe radius $R_{\rm L}$ concept in order to treat stars in binary systems. If the stellar companion is approaching its $R_{\rm L}$, mass transfer treatment is initiated. However, the effective acceleration also affects the evolution of a star in a close binary system. This is different from the gravity inside a single star, whether that single star is rotating or not. Here, we present numerically obtained tables of properties of stars in a binary system as a function of the effective potential: volume-equivalent radii of the equipotential surfaces, effective accelerations and the inverse effective accelerations averaged over the same equipotential surfaces, and the properties of the L1 plane cross-sections. The tables are obtained for binaries where the ratios of the primary star mass to the companion star mass are from $10^{-6}$ to $10^5$ and include equipotential surfaces up to the star's outer Lagrangian point. We describe the numerical methods used to obtain these quantities and report how we verified the numerical results. We also describe and verify the method to obtain the effective acceleration for non-point mass distributions. We supply a sample code showing how to use our tables to get the average effective accelerations in one-dimensional stellar codes.

Authors:S. Torres, P. Cruz, R. Murillo-Ojeda, F. M. Jiménez-Esteban, A. Rebassa-Mansergas, E. Solano, M. E. Camisassa, R. Raddi, J. Doliguez Le Lourec

Abstract: The characterization of white dwarf atmospheres is crucial for accurately deriving stellar parameters such as effective temperature, mass, and age. We aim to classify the population of white dwarfs up to 500 pc into hydrogen-rich or hydrogen-deficient atmospheres based on Gaia spectra and to derive an accurate spectral type-temperature distribution of white dwarfs as a function of the effective temperature for the largest observed unbiased sample of these objects. We took advantage of the recent Gaia low-resolution spectra available for 76,657 white dwarfs up to 500 pc. We calculated synthetic J-PAS narrow-band photometry and fitted the spectral energy distribution of each object with up-to-date models for hydrogen-rich and helium-rich white dwarf atmospheres. We estimated the probability for a white dwarf to have a hydrogen-rich atmosphere and validated the results using the Montreal White Dwarf Database. Finally, precise effective temperature values were derived for each object using La Plata evolutionary models. We have successfully classified a total of 65,310 white into DAs and non-DAs with an accuracy of 94%. An unbiased subsample of nearly 34,000 objects was built, from which we computed a precise spectral distribution spanning an effective temperature range from 5,500 to 40,000 K, while accounting for potential selection effects. Some characteristic features of the spectral evolution, such as the deficit of helium-rich stars at T_eff $\approx$35,000-40,000 K and in the range 22,000 < T_eff < 25,000 K, as well as a gradual increase from 18,000K to T_eff $\approx$7,000K, where the non-DA stars percentage reaches its maximum of 41%, followed by a decrease for cooler temperatures, are statistically significant. These findings will provide precise constraints for the proposed models of spectral evolution.

Authors:Bea Zenteno-Quinteros, Pablo S Moya, Marian Lazar, Adolfo F Vinas, Stefaan Poedts

Abstract: Temperature anisotropy and field-aligned skewness are commonly observed non-thermal features in electron velocity distributions in the solar wind. These characteristics can act as a source of free energy to destabilize different electromagnetic wave modes, which may alter the plasma state through wave-particle interactions. Previous theoretical studies have mainly focused on analyzing these non-thermal features and self-generated instabilities individually. However, to obtain a more accurate and realistic understanding of kinetic processes in the solar wind, it is necessary to examine the interplay between these two energy sources. By means of linear kinetic theory, in this paper we investigate the excitation of the parallel-propagating whistler mode, when it is destabilized by electron populations exhibiting both temperature anisotropy and field-aligned strahl or skewness. To describe the solar wind electrons, we adopt the Core-Strahlo model as an alternative approach. This model offers the advantage of representing the suprathermal features of halo and strahl electrons, using a single skew-Kappa distribution already known as the strahlo population. Our findings show that when the electron strahlo exhibits an intrinsic temperature anisotropy, this suprathermal population becomes a stronger and more efficient source of free energy for destabilizing the whistler mode. This suggests a greater involvement of the anisotropic strahlo in processes conditioned by wave-particle interactions. Present results also suggest that the contribution of core anisotropy can be safely disregarded when assessing the importance of instabilities driven by the suprathermal population. This allows for a focused study, particularly regarding the regulation of electron heat flux in the solar wind.

Authors:De-Chao Song, Jun Tian, Y. Li, M. D. Ding, Yang Su, Sijie Yu, Jie Hong, Ye Qiu, Shihao Rao, Xiaofeng Liu, Qiao Li, Xingyao Chen, Chuan Li, Cheng Fang

Abstract: The heating mechanisms of solar white-light flares remain unclear. We present an X1.0 white-light flare on 2022 October 2 (SOL2022-10-02T20:25) observed by the Chinese \ha\ Solar Explorer (CHASE) that provides two-dimensional spectra in the visible light for the full solar disk with a seeing-free condition. The flare shows a prominent enhancement of $\sim$40\% in the photospheric \fe\ line at 6569.2 \AA, and the nearby continuum also exhibits a maximum enhancement of $\sim$40\%. For the continuum near the \fe\ line at 6173 \AA\ from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), it is enhanced up to $\sim$20\%. At the white-light kernels, the \fe\ line at 6569.2 \AA\ has a symmetric Gaussian profile that is still in absorption and the H$\alpha$ line at 6562.8 \AA\ displays a very broad emission profile with a central reversal plus a red or blue asymmetry. The white-light kernels are co-spatial with the microwave footpoint sources observed by the Expanded Owens Valley Solar Array (EOVSA) and the time profile of the white-light emission matches that of the hard X-ray emission above 30 keV from the Gamma-ray Burst Monitor (GBM) on Fermi. These facts indicate that the white-light emission is qualitatively related to a nonthermal electron beam. We also perform a radiative hydrodynamic simulation with the electron beam parameters constrained by the hard X-ray observations from Fermi/GBM. The result reveals that the white-light enhancement cannot be well explained by a pure electron-beam heating together with its induced radiative backwarming but may need additional heating sources such as \alfven\ waves.

Authors:F. Kahraman Alicavus, G. C. Coban, E. Celik, D. S. Dogan, O. Ekinci, F. Alicavus

Abstract: The presence of pulsating stars in eclipsing binary systems (EBs) makes these objects significant since they allow us to investigate the stellar interior structure and evolution. Different types of pulsating stars could be found in EBs such as Delta Scuti variables. Delta Scuti stars in EBs have been known for decades and the increasing number of such systems is important for understanding pulsational structure. Hence, in this study, a research was carried out on the southern TESS field to discover new Delta Scuti stars in EBs. We produced an algorithm to search for detached and semi-detached EBs considering three steps; the orbital period (P$_{orb}$)'s harmonics in the Fourier spectrum, skewness of the light curves, and classification of \textsc{UPSILON} program. If two of these steps classify a system as an EB, the algorithm also identifies it as an EB. The TESS pixel files of targets were also analyzed to see whether the fluxes are contaminated by other systems. No contamination was found. We researched the existence of pulsation through EBs with a visual inspection. To confirm Delta Scuti-type oscillations, the binary variation was removed from the light curve, and residuals were analyzed. Consequently, we identified 42 Delta Scuti candidates in EBs. The P$_{orb}$, $L$, and M$_{V}$ of systems were calculated. Their positions on the H-R diagram and the known orbital-pulsation period relationship were analyzed. We also examined our targets to find if any of them show frequency modulation with the orbital period and discovered one candidate of tidally tilted pulsators.

Authors:A. Feeney-Johansson, S. J. D. Purser, T. P. Ray, C. Carrasco-González, A. Rodríguez-Kamenetzky, J. Eislöffel, J. Lim, R. Galván-Madrid, S. Lizano, L. F. Rodríguez, H. Shang, P. Ho, M. Hoare

Abstract: Using observations with e-MERLIN and the VLA, together with archival data from ALMA, we obtain high-resolution radio images of two binary YSOs: L1551 IRS 5 and L1551 NE, covering a wide range of frequencies from 5 - 336 GHz, and resolving emission from the radio jet on scales of only ~15 au. By comparing these observations to those from a previous epoch, it is shown that there is a high degree of variability in the free-free emission from the jets of these sources. In particular, the northern component of L1551 IRS 5 shows a remarkable decline in flux density of a factor of ~5, suggesting that the free-free emission of this source has almost disappeared. By fitting the spectra of the sources, the ionised mass-loss rates of the jets are derived and it is shown that there is significant variability of up to a factor of ~6 on timescales of ~20 years. Using radiative transfer modelling, we also obtained a model image for the jet of the southern component of L1551 IRS 5 to help study the inner region of the ionised high-density jet. The findings favour the X-wind model launched from a very small innermost region.

Authors:Nikita Rawat, J. C. Pandey, Arti Joshi, Srinivas M Rao, Michaël De Becker

Abstract: We present the preliminary timing analysis of confirmed intermediate polar UU Col and possible intermediate polar Swift J0939.7-3224 in the optical band with the help of long-term, high-cadence continuous photometry from Transiting Exoplanet Survey Satellite (TESS). For UU Col, we revise previously reported orbital and spin periods as 3.464 $\pm$ 0.005 h and 863.74 $\pm$ 0.08 s, respectively. Using the second harmonic of the beat frequency, the beat period is estimated as $\sim$928 s. These findings indicate that UU Col is a disc-fed dominated disc-overflow accretor. For J0939, we establish the spin period as 2671.8 $\pm$ 0.8 s and refine the provisionally suggested orbital period as 8.49 $\pm$ 0.03 h. The absence of beat frequency in J0939 signifies that it might be a pure disc-fed accretor; however, an X-ray study of this source will help to understand its true nature.

Authors:Rui Wang, Ying D. Liu, Xiaowei Zhao, Huidong Hu

Abstract: Small-scale eruptions could play an important role in coronal heating, generation of solar energetic particles (SEPs), and mass source of the solar wind. However, they are poorly observed, and their characteristics, distributions, and origins remain unclear. Here a mini coronal dimming was captured by the recently launched Solar Orbiter spacecraft. The observations indicate that a minifilament eruption results in the dimming and takes away approximately $(1.65\pm0.54)\times10^{13}$ g of mass, which also exhibits similar features as the sources of SEP events. The released magnetic free energy is of the order of $\sim10^{27}$ erg. Our results suggest that weak constraining force makes the flux rope associated with the minifilament easily enter a torus-unstable domain. We discuss that weak magnetic constraints from low-altitude background fields may be a general condition for the quiet-Sun eruptions, which provide a possible mechanism for the transport of coronal material and energy from the lower to the middle or even higher corona.

Authors:Han He, Weitao Zhang, Haotong Zhang, Song Wang, Ali Luo, Jun Zhang

Abstract: Distribution of stellar $\mathrm{H}\alpha$ chromospheric activity with respect to stellar atmospheric parameters (effective temperature $T_\mathrm{eff}$, surface gravity $\log\,g$, and metallicity $\mathrm{[Fe/H]}$) and main-sequence/giant categories is investigated for the F-, G-, and K-type stars observed by the LAMOST Medium-Resolution Spectroscopic Survey (MRS). A total of 329,294 MRS spectra from LAMOST DR8 are utilized in the analysis. The $\mathrm{H}\alpha$ activity index ($I_{\mathrm{H}{\alpha}}$) and the $\mathrm{H}\alpha$ $R$-index ($R_{\mathrm{H}{\alpha}}$) are evaluated for the MRS spectra. The $\mathrm{H}\alpha$ chromospheric activity distributions with individual stellar parameters as well as in the $T_\mathrm{eff}$ -- $\log\,g$ and $T_\mathrm{eff}$ -- $\mathrm{[Fe/H]}$ parameter spaces are analyzed based on the $R_{\mathrm{H}{\alpha}}$ index data. It is found that: (1) for the main-sequence sample, the $R_{\mathrm{H}{\alpha}}$ distribution with $T_\mathrm{eff}$ has a bowl-shaped lower envelope with a minimum at about 6200 K, a hill-shaped middle envelope with a maximum at about 5600 K, and an upper envelope continuing to increase from hotter to cooler stars; (2) for the giant sample, the middle and upper envelopes of the $R_{\mathrm{H}{\alpha}}$ distribution first increase with decrease of $T_\mathrm{eff}$ and then drop to a lower activity level at about 4300 K, revealing the different activity characteristics at different stages of stellar evolution; (3) for both the main-sequence and giant samples, the upper envelope of the $R_{\mathrm{H}{\alpha}}$ distribution with metallicity is higher for stars with $\mathrm{[Fe/H]}$ greater than about $-1.0$, and the lowest-metallicity stars hardly exhibit high $\mathrm{H}\alpha$ indices. A dataset of $\mathrm{H}\alpha$ activity indices for the LAMOST MRS spectra analyzed is provided with this paper.

Authors:C. Swastik, Ravinder K. Banyal, Mayank Narang, Athira Unni, Bihan Banerjee, P. Manoj, T. Sivarani

Abstract: The GAIA space mission is impacting astronomy in many significant ways by providing a uniform, homogeneous and precise data set for over 1 billion stars and other celestial objects in the Milky Way and beyond. Exoplanet science has greatly benefited from the unprecedented accuracy of stellar parameters obtained from GAIA. In this study, we combine photometric, astrometric, and spectroscopic data from the most recent Gaia DR3 to examine the kinematic and chemical age proxies for a large sample of 2611 exoplanets hosting stars whose parameters have been determined uniformly. Using spectroscopic data from the Radial Velocity Spectrometer (RVS) onboard GAIA, we show that stars hosting massive planets are metal-rich and $\alpha$-poor in comparison to stars hosting small planets. The kinematic analysis of the sample reveals that the stellar systems with small planets and those with giant planets differ in key aspects of galactic space velocity and orbital parameters, which are indicative of age. We find that the galactic orbital parameters have a statistically significant difference of 0.06 kpc for $Z_{max}$ and 0.03 for eccentricity respectively. Furthermore, we estimated the stellar ages of the sample using the MIST-MESA isochrone models. The ages and its proxies for the planet-hosting stars indicate that the hosts of giant planetary systems are younger compared to the population of stars harboring small planets. These age trends are also consistent with the chemical evolution of the galaxy and the formation of giant planets from the core-accretion process.

Authors:Vipin Kumar, A. S. Rajpurohit, Mudit K. Srivastava, José G. Fernández-Trincado, A. B. A. Queiroz

Abstract: The time scales of variability in active M dwarfs can be related to their various physical parameters. Thus, it is important to understand such variability to decipher the physics of these objects. In this study, we have performed the low resolution ($\sim$5.7\AA) spectroscopic monitoring of 83 M dwarfs (M0-M6.5) to study the variability of H$\alpha$ / H$\beta$ emissions; over the time scales from $\sim$0.7 to 2.3 hours with a cadence of $\sim$3-10 minutes. Data of a sample of another 43 late-type M dwarfs (M3.5-M8.5) from the literature are also included to explore the entire spectral sequence. 53 of the objects in our sample ($\sim$64\%) show statistically significant short-term variability in H$\alpha$. We show that this variability in 38 of them are most likely to be related to the flaring events. We find that the early M dwarfs are less variable despite showing higher activity strengths (L$_{H\alpha}$/L$_{bol}$ \& L$_{H\beta}$/L$_{bol}$), which saturates around $\sim$10$^{-3.8}$ for M0-M4 types. Using archival photometric light curves from TESS and Kepler/K2 missions, the derived chromospheric emission (\ha and \hb emission) variability is then explored for any plausible systematics with respect to their rotation phase. The variability indicators clearly show higher variability in late-type M dwarfs (M5-M8.5) with shorter rotation periods ($<$2 days). For 44 sources, their age has been estimated using StarHorse project and possible correlations with variability have been explored. The possible causes and implications for these behaviors are discussed.

Authors:Y. J. Aidelman, M. Borges Fernandes, L. S. Cidale, A. Smith Castelli, M. L. Arias, J. Zorec, M. Kraus, A. Torres, T. B. Souza, Y. R. Cochetti

Abstract: Context. Stars in transition phases, like those showing the B[e] phenomenon and luminous blue variables (LBVs), undergo strong, often irregular mass ejection events. The prediction of these phases in stellar evolution models is therefore extremely difficult if not impossible. As a result, their effective temperatures, their luminosities and even their true nature are not fully known. Aims. A suitable procedure to derive the stellar parameters of these types of objects is to use the BCD spectrophotometric classification system, based on the analysis of the Balmer discontinuity. The BCD parameters ({\lambda}_1, D) are independent of interstellar extinction and circumstellar contributions. Methods. We obtained low-resolution spectra for 14 stars with the B[e] phenomenon and LBVs. Using the BCD method, we derived the stellar and physical parameters. The study was complemented with the information provided by the JHK colour-colour diagram. Results. For each star, the BCD system gives a complete set of fundamental parameters and related quantities such as luminosity and distance. We confirmed HK Ori, HD 323771 and HD 52721 as pre-main sequence HAe/B[e], AS 202 and HD 85567 as FS CMa-type, and HD 62623 as sgB[e] stars. We classified Hen 3-847, CD-24 5721, and HD 53367 as young B[e] stars or FS CMa-type candidates, and HD 58647 as a slightly evolved B[e] star. In addition, Hen 3-1398 is an sgB[e] and MWC 877, CPD-59 2854 and LHA 120-S 65 are LBV candidates. The stellar parameters of the latter two LBVs are determined for the first time. Conclusions. Our results emphasise that the BCD system is a highly valuable tool to derive stellar parameters and physical properties of B-type stars in transition phases. This method can be combined with near-IR colour-colour diagrams to determine or confirm the evolutionary stage of emission-line stars with dust disks.

Authors:Catia Grimani, Vincenzo Andretta, Ester Antonucci, Paolo Chioetto, Vania Da Deppo, Michele Fabi, Samuel Gissot, Giovanna Jerse, Mauro Messerotti, Giampiero Naletto, Mauruzio Pancrazzi, Andrea Persici, Christina Plainaki, Marco Romoli, Federico Sabbatini, Daniele Spadaro, Marco Stangalini, Daniele Telloni, Luca Teriaca, Michela Uslenghi, Mattia Villani, Lucia Abbo, Aleksandr Burtovoi, Federica Frassati, Federico Landini, Giana Nicolini, Giuliana Russano, Clementina Sasso, Roberto Susino

Abstract: Context. Galactic cosmic rays (GCRs) and solar particles with energies greater than tens of MeV penetrate spacecraft and instruments hosted aboard space missions. The Solar Orbiter Metis coronagraph is aimed at observing the solar corona in both visible (VL) and ultraviolet (UV) light. Particle tracks are observed in the Metis images of the corona. An algorithm has been implemented in the Metis processing electronics to detect the VL image pixels crossed by cosmic rays. This algorithm was initially enabled for the VL instrument only, since the process of separating the particle tracks in the UV images has proven to be very challenging. Aims. We study the impact of the overall bulk of particles of galactic and solar origin on the Metis coronagraph images. We discuss the effects of the increasing solar activity after the Solar Orbiter mission launch on the secondary particle production in the spacecraft. Methods. We compared Monte Carlo simulations of GCRs crossing or interacting in the Metis VL CMOS sensor to observations gathered in 2020 and 2022. We also evaluated the impact of solar energetic particle events of different intensities on the Metis images. Results. The study of the role of abundant and rare cosmic rays in firing pixels in the Metis VL images of the corona allows us to estimate the efficiency of the algorithm applied for cosmic-ray track removal from the images and to demonstrate that the instrument performance had remained unchanged during the first two years of the Solar Orbiter operations. The outcome of this work can be used to estimate the Solar Orbiter instrument's deep charging and the order of magnitude for energetic particles crossing the images of Metis and other instruments such as STIX and EUI.

Authors:Pallavi Saraf IIA, Carlos Allende Prieto, Thirupathi Sivarani, Avrajit Bandyopadhyay, Timothy C. Beers, A. Susmitha

Abstract: There has been a concerted effort in recent years to identify the astrophysical sites of the $r$-process that can operate early in the Galaxy. The discovery of many $r$-process-enhanced (RPE) stars (especially by the $R$-process Alliance collaboration) has significantly accelerated this effort. However, only limited data exist on the detailed elemental abundances covering the primary neutron-capture peaks. Subtle differences in the structure of the $r$-process pattern, such as the relative abundances of elements in the third peak, in particular, are expected to constrain the $r$-process sites further. Here, we present a detailed elemental-abundance analysis of four bright RPE stars selected from the HESP-GOMPA survey. Observations were carried out with the 10-m class telescope Gran Telescopio Canarias (GTC), Spain. The high spectral signal-to-noise ratios obtained allow us to derive abundances for 20 neutron-capture elements, including the third $r$-process peak element osmium (Os). We detect thorium (Th) in two stars, which we use to estimate their ages. We discuss the metallicity evolution of Mg, Sr, Ba, Eu, Os, and Th in $r$-II and $r$-I stars, based on a compilation of RPE stars from the literature. The strontium (Sr) abundance trend with respect to europium (Eu) suggests the need for an additional production site for Sr (similar to several earlier studies); this requirement could be milder for yttrium (Y) and zirconium (Zr). We also show that there could be some time delay between $r$-II and $r$-I star formation, based on the Mg/Th abundance ratios.

Authors:N. P. Ikonnikova, M. A. Burlak, A. V. Dodin, A. A. Belinski, A. M. Tatarnikov, N. A. Maslennikova, S. G. Zheltoukhov, K. E. Atapin

Abstract: The observations and comprehensive study of intermediate initial mass stars at the late stages of evolution, and after the asymptotic giant branch (AGB) in particular, are of crucial importance to identify the common properties for the stars of given group and to reveal binaries among them. This work aims to investigate photometric and spectral peculiarities of a poorly studied post-AGB candidate and infrared source IRAS 07253-2001. We present the new multicolour $UBVR_{C}I_{C}YJHK$ photometry obtained with the telescopes of the Caucasian mountain observatory and analyse it together with the data acquired by the All Sky Automated Survey for SuperNovae. We report on the detection of multiperiod brightness variability caused by pulsations. A beating of close periods, the main one of 73 days and additional ones of 68 and 70 days, leads to amplitude variations. We have also detected a long-term sine trend in brightness with a period of nearly 1800 days. We suppose it to be orbital and IRAS 07253-2001 to be binary. Based on new low-resolution spectroscopic data obtained with the 2.5-m telescope of the Caucasian mountain observatory in 2020 and 2023 in the $\lambda$3500-7500 wavelength range we have identified spectral lines and compiled a spectral atlas. We have found the [N II], [Ni II] and [S II] forbidden emission lines in the spectrum and discuss their origin. The H$\alpha$ line has a variable double-peaked emission component. We have derived preliminary estimates of the star's parameters and detected a variation of radial velocity with a peak-to-peak amplitude of about 30 km s$^{-1}$.

Authors:David Gruner, Sydney A. Barnes, Kenneth A. Janes

Abstract: Gyrochronology enables the derivation of ages of late-type main sequence stars based on their rotation periods and a mass proxy, such as color. It has been explored in open clusters, but a connection to field stars has yet to be successfully established. We explore the rotation rates of wide binaries, representing enlightening intermediaries between clusters and field stars, and their overlap with those of open cluster stars. We investigated a recently created catalog of wide binaries, matched the cataloged binaries to observations by the Kepler mission (and its K2 extension), validated or re-derived their rotation periods, identified 283 systems where both stars are on the main sequence and have vetted rotation periods, and compared the systems with open cluster data. We find that the vast majority of these wide binaries (236) line up directly along the curvilinear ribs defined by open clusters in color-period diagrams or along the equivalent interstitial gaps between successive open clusters. The parallelism in shape is remarkable. Twelve additional systems are clearly rotationally older. The deviant systems, a minority, are mostly demonstrably hierarchical. Furthermore, the position of the evolved component in the color-magnitude diagram for the additional wide binary systems that contain one is consistent with the main sequence component's rotational age. We conclude that wide binaries, despite their diversity, follow the same spindown relationship as observed in open clusters, and we find that rotation-based age estimates yield the same ages for both components in a wide binary. This suggests that cluster and field stars spin down in the same way and that gyrochronology can be applied to field stars to determine their ages, provided that they are sufficiently distant from any companions to be considered effectively single.

Authors:Thibaut Dumont

Abstract: Asteroseismology provides a unique opportunity to probe the interiors of evolved stars and constrain their internal rotation. The correct reproduction of the core rotation evolution is key to understanding the internal processes involved in low-mass stars. We explore the efficiency required to reproduce the behaviour of the transport of angular momentum (AM) in view of asteroseismic constraints. We computed a series of models and investigated an updated AM transport by including a time-dependent extra viscosity related to the AMRI. We compared our predictions to the asteroseismic measurements of the core and surface rotation of a sample of SGB and RGB stars. We confirm that a time-dependent additional viscosity is required to reproduce the general behaviour of the core rotation rate along evolution. We show that it results in stronger Li and Be depletions for low-mass stars over evolution. We confirm that predicted Li abundances at the RGB bump by classical models, commonly used as references, cannot reproduce the Li depletion along the MS and evolved phases of stellar evolution. We show that the observed amount of Li of stars less massive than 1Msun leads to a discrepancy between model predictions and observations at the RGB bump. We show that a semi-parametric model can reproduce the rotational behaviour along the first phases of evolution well, with the exception of the sharp transition observed during the SGB phase. This suggests that two distinct transport processes may be involved. The processes required to transport chemicals during the MS, and AM until the RGB phase impact the Li depletion all along the evolutionary duration. A good prediction of the Li abundance at young phases places strong constraints on the predicted one at more evolved phases. It also impacts the threshold that defines Li-rich giant stars, showing that classical models tend to overestimate its value.

Authors:S. W. Good, O. K. Rantala, A. -S. M. Jylhä, C. H. K. Chen, C. Möstl, E. K. J. Kilpua

Abstract: Interplanetary coronal mass ejections (ICMEs) have low proton beta across a broad range of heliocentric distances and a magnetic flux rope structure at large scales, making them a unique environment for studying solar wind fluctuations. Power spectra of magnetic field fluctuations in 28 ICMEs observed between 0.25 and 0.95 au by Solar Orbiter and Parker Solar Probe have been examined. At large scales, the spectra were dominated by power contained in the flux ropes. Subtraction of the background flux rope fields reduced the mean spectral index from $-5/3$ to $-3/2$ at $kd_i \leq 10^{-3}$. Rope subtraction also revealed shorter correlation lengths in the magnetic field. The spectral index was typically near $-5/3$ and radially invariant in the inertial range regardless of rope subtraction, and steepened to values consistently below $-3$ with transition to kinetic scales. The high-frequency break point terminating the inertial range evolved almost linearly with radial distance and was closer in scale to the proton inertial length than the proton gyroscale, as expected for plasma at low proton beta. Magnetic compressibility at inertial scales did not grow with radial distance, in contrast to the solar wind generally. In ICMEs, the distinctive spectral properties at injection scales appear mostly determined by the global flux rope structure while transition-kinetic properties are more influenced by the low proton beta; the intervening inertial range appears independent of both ICME features, indicative of a system-independent scaling of the turbulence.

Authors:G. Valori, D. Calchetti, A. Moreno Vacas, É. Pariat, S. K. Solanki, P. Löschl, J. Hirzberger, S. Parenti, K. Albert, N. Albelo Jorge, A. Álvarez-Herrero, T. Appourchaux, L. R. Bellot Rubio, J. Blanco Rodríguez, A. Campos-Jara, A. Feller, A. Gandorfer, P. García Parejo, D. Germerott, L. Gizon, J. M. Gómez Cama, L. Guerrero, P. Gutierrez-Marques, F. Kahil, M. Kolleck, A. Korpi-Lagg, D. Orozco Suárez, I. Pérez-Grande, E. Sanchis Kilders, J. Schou, U. Schühle, J. Sinjan, J. Staub, H. Strecker, J. C. del Toro Iniesta, R. Volkmer, J. Woch

Abstract: Spectropolarimetric reconstructions of the photospheric vector magnetic field are intrinsically limited by the 180$^\circ$-ambiguity in the orientation of the transverse component. So far, the removal of such an ambiguity has required assumptions about the properties of the photospheric field, which makes disambiguation methods model-dependent. The basic idea is that the unambiguous line-of-sight component of the field measured from one vantage point will generally have a non-zero projection on the ambiguous transverse component measured by the second telescope, thereby determining the ``true'' orientation of the transverse field. Such an idea was developed and implemented in the Stereoscopic Disambiguation Method (SDM), which was recently tested using numerical simulations. In this work we present a first application of the SDM to data obtained by the High Resolution Telescope (HRT) onboard Solar Orbiter during the March 2022 campaign, when the angle with Earth was 27 degrees. The method is successfully applied to remove the ambiguity in the transverse component of the vector magnetogram solely using observations (from HRT and from the Helioseismic and Magnetic Imager), for the first time. The SDM is proven to provide observation-only disambiguated vector magnetograms that are spatially homogeneous and consistent. A discussion about the sources of error that may limit the accuracy of the method, and of the strategies to remove them in future applications, is also presented.

Authors:K. Mori, H. Hotta

Abstract: In this work, we systematically investigate the scale-dependent angular momentum flux by analysing high-resolution three-dimensional magnetohydrodynamic simulations in which the solar-like differential rotation is reproduced without using any manipulations. More specifically, the magnetic angular momentum transport (AMT) plays a dominant role in the calculations. We examine the important spatial scales for the magnetic AMT. The main conclusions of our approach can be summarized as follows: 1. Turbulence transports the angular momentum radially inward. This effect is more pronounced in the highest resolution calculation. 2. The dominant scale for the magnetic AMT is the smallest spatial scale. 3. The dimensionless magnetic correlation is low in the high-resolution simulation. Thus, chaotic but strong small-scale magnetic fields achieve efficient magnetic AMT.

Authors:A. P. Milone, G. Cordoni, A. F. Marino, F. Muratore, F. D'Antona, M. Di Criscienzo, E. Dondoglio, E. P. Lagioia, M. V. Legnardi, A. Mohandasan, T. Ziliotto, F. Dell'Agli, M. Tailo, P. Ventura

Abstract: Young and intermediate-age star clusters of both Magellanic Clouds exhibit complex color-magnitude diagrams. In addition to the extended main-sequence turn-offs (eMSTOs), commonly observed in star clusters younger than ~2 Gyr, the clusters younger than ~800 Myr exhibit split main sequences (MSs). These comprise a blue MS, composed of stars with low-rotation rates, and a red MS, which hosts fast-rotating stars. While it is widely accepted that stellar populations with different rotation rates are responsible for the eMSTOs and split MSs, their formation and evolution are still debated. A recent investigation of the ~1.7 Gyr old cluster NGC1783 detected a group of eMSTO stars extremely dim in UV bands. Here, we use multi-band Hubble Space Telescope photometry to investigate five star clusters younger than ~200 Myr, including NGC1805, NGC1818, NGC1850, and NGC2164 in the Large Magellanic Cloud, and the Small-Magellanic Cloud cluster NGC330. We discover a group of bright MS stars in each cluster that are significantly dim in the F225W and F275W bands, similar to what is observed in NGC1783. Our result suggests that UV-dim stars are common in young clusters. The evidence that most of them populate the blue MS indicates that they are slow rotators. As a byproduct, we show that the star clusters NGC1850 and BHRT5b exhibit different proper motions, thus corroborating the evidence that they are not gravitationally bound.

Authors:Abbigail K. Elms, Pier-Emmanuel Tremblay, Boris T. Gänsicke, Andrew Swan, Carl Melis, Antoine Bédard, Christopher J. Manser, James Munday, J. J. Hermes, Erik Dennihy, Atsuko Nitta, Ben Zuckerman

Abstract: Two recently discovered white dwarfs, WDJ041246.84$+$754942.26 and WDJ165335.21$-$100116.33, exhibit H$\alpha$ and H$\beta$ Balmer line emission similar to stars in the emerging DAHe class, yet intriguingly have not been found to have detectable magnetic fields. These white dwarfs are assigned the spectral type DAe. We present detailed follow-up of the two known DAe stars using new time-domain spectroscopic observations and analysis of the latest photometric time-series data from TESS and ZTF. We measure the upper magnetic field strength limit of both stars as $B < 0.05$ MG. The DAe white dwarfs exhibit photometric and spectroscopic variability, where in the case of WDJ041246.84$+$754942.26 the strength of the H$\alpha$ and H$\beta$ emission cores varies in anti-phase with its photometric variability over the spin period, which is the same phase relationship seen in DAHe stars. The DAe white dwarfs closely cluster in one region of the Gaia Hertzsprung-Russell diagram together with the DAHe stars. We discuss current theories on non-magnetic and magnetic mechanisms which could explain the characteristics observed in DAe white dwarfs, but additional data are required to unambiguously determine the origin of these stars.

Authors:Yoichi Takeda

Abstract: IW Per, a single-lined spectroscopic binary with a short period of 0.92d, is known to be a A-type metallic-line (Am) star showing anomalous line strengths of specific elements. Previously, Kim (1980) reported that its equivalent widths of CaII 3934, SrII 4215, and ScII 4320 lines (important key lines characterizing the Am anomaly) show cyclic variations in accordance with the rotation phase, implyig that the chemical peculiarities on the surface are not uniform but of rather patchy distribution, though no trial of reconfirmation seems to have been done so far. In order to check the validity of this finding, 10 high-dispesion spectra of IW Per covering different phases were analyzed for these lines by using the spectrum-fitting technique to determine the abundances of Ca, Sr, and Sc and the corresponding equivalent widths. It turned out, however, that no firm evidence of such phase-dependent line-strength variations could be found, suggesting that significant chemical inhomogeneity on the surface of IW Per is unlikely to exist, at least as regards to the period of our observations (2010 December). Meanwhile, the abundances of O, Si, Ca, Ba, and Fe resulting from the 6130-6180A region corroborate that IW Per is a distinct Am star despite that its rotational velocity (~100 km/s) is near to the existent limit of Am phenomenon.

Authors:Loren I. Matilsky

Abstract: The lowest-order force balance in rotating stars is between gravity, pressure, and the centrifugal force (here referred to as 'GPR' balance). GPR balance determines both the stellar oblateness and the aspherical thermal anomalies. Here we emphasize a subtle point. Stellar thermal wind balance is simply the curl of GPR balance and the stellar thermal wind should be regarded as the baroclinic component of the oblateness. The thermal wind thus determines only part of the aspherical thermal anomalies, which have both baroclinic and barotropic contributions. Here we treat the full oblateness, including the thermal wind, using pressure coordinates. We derive the generalised stellar thermal wind equation and identify the parameter regime for which it holds. In the case of the Sun, not including the oblateness has resulted in conflicting calculations of the theoretical aspherical temperature anomaly. We provide new calculation here and find that the baroclinic anomaly from the thermal wind is ~3-60 times smaller than the barotropic anomaly and may not be measurable helioseismically. If measurement were possible, this would potentially yield a new way to bracket the depth of the solar tachocline.

Authors:Thayse A. Pacheco, Ronaldo S. Levenhagen, Marcos P. Diaz, Paula R. T. Coelho

Abstract: We present an update of the grid of detailed atmosphere models and homogeneous synthetic spectra for hot, high-gravity subdwarf stars. High-resolution spectra and synthetic photometry were calculated in the wavelength range 1,000 \r{A} - 10,000 \r{A} using Non-LTE extensively line-blanketed atmosphere structures.

Authors:Małgorzata Pietras, Robert Falewicz, Marek Siarkowski, Anna Kepa, Kamil Bicz, Paweł Preś

Abstract: We present an analysis of a flare on the Wolf 359 star based on simultaneous observations of TESS and XMM-Newton. A stellar flare with energy comparable to an X-class solar flare is analyzed on this star for the first time. The main goal of the study was to determine whether the same physical processes drive and occur in stellar flares as in the solar flares. We tried to estimate the flare class by various direct and indirect methods. Light curves and spectra in different energy ranges were used to determine the parameters and profiles of the flare. From the XMM-Newton EPIC-pn X-ray data, we estimated the temperature and emission measure during the flare. The thermodynamical timescale and the loop semi-length were also determined with two different methods. The RGS spectra enabled us to calculate the differential emission measure (DEM) distributions. The obtained DEM distributions have three components at temperature values of 3 MK, 7 MK, and 16-17 MK. The analysis of the line ratio in helium-like triplets allowed us to determine the plasma electron density. Our results for the flare loop on Wolf 359 were compared to typical parameters for solar flares observed with GOES and RHESSI. This supports our conclusion that the processes taking place in stellar flares are like those in solar flares. The determined geometrical parameters of the phenomenon do not differ from the values of analogs occurring on the Sun.

Authors:Maksym Ersteniuk, Timothy Banks, Edwin Budding

Abstract: Model orbits have been fitted to 27 physical double stars listed in the 1922 catalogue of Miller & Pitman (MP). A Markov Chain Monte Carlo technique was applied to estimate best fitting values and associated uncertainties for the orbital parameters. Dynamical masses were calculated using parallaxes from the Hipparcos and Gaia missions. These are not in strong agreement with the masses given by MP. This is surprising given the high correlation between the parallaxes from these missions and those listed by MP; unfortunately calculations are not given by MP nor are orbital parameters. The results of the current study are in good agreement with a recent study, as are comparisons with the orbital parameters listed by the Washington Double Star catalog, confirming the validity of the MCMC modelling.

Authors:Luc Dessart, W. V. Jacobson-Galán

Abstract: A large fraction of red-supergiant stars seem to be enshrouded by circumstellar material (CSM) at the time of explosion. Relative to explosions in a vacuum, this CSM causes both a luminosity boost at early times as well as the presence of symmetric emission lines with a narrow core and electron-scattering wings typical of type IIn supernovae (SNe). For this study, we performed radiation-hydrodynamics and radiative transfer calculations for a variety of CSM configurations (i.e., compact, extended, and detached) and documented the resulting ejecta and radiation properties. We find that models with a dense, compact, and massive CSM of ~0.5Msun can match the early luminosity boost of type II-P SNe but fail to produce type IIn-like spectral signatures (aka ``flash features''). These only arise if the photon mean free path in the CSM is large enough (i.e, if the density is low enough) to allow for a radiative precursor through a long-lived (i.e., a day to a week), radially extended unshocked optically thick CSM. The greater radiative losses and kinetic-energy extraction in this case boost the luminosity even for modest CSM masses -- this boost is delayed for a detached CSM. The inadequate assumption of high CSM density, in which the shock travels quasi adiabatically, overestimates the CSM mass and associated mass-loss rate. Our simulations also indicate that type IIn-like spectral signatures last as long as there is optically-thick unshocked CSM. Constraining the CSM structure therefore requires a combination of light curves and spectra, rather than photometry alone. We emphasize that for a given total energy, the radiation excess fostered by the presence of CSM comes at the expense of kinetic energy, as evidenced by the disappearance of the fastest ejecta material and the accumulation of mass in a dense shell. Both effects can be constrained from spectra well after the interaction phase.

Authors:Christine E. Collins, Stuart A. Sim, Luke. J. Shingles, Sabrina Gronow, Friedrich K. Roepke, Ruediger Pakmor, Ivo R. Seitenzahl, Markus Kromer

Abstract: The double detonation is a widely discussed mechanism to explain Type Ia supernovae from explosions of sub-Chandrasekhar mass white dwarfs. In this scenario, a helium detonation is ignited in a surface helium shell on a carbon/oxygen white dwarf, which leads to a secondary carbon detonation. Explosion simulations predict high abundances of unburnt helium in the ejecta, however, radiative transfer simulations have not been able to fully address whether helium spectral features would form. This is because helium can not be sufficiently excited to form spectral features by thermal processes, but can be excited by collisions with non-thermal electrons, which most studies have neglected. We carry out a full non-local thermodynamic equilibrium (non-LTE) radiative transfer simulation for an instance of a double detonation explosion model, and include a non-thermal treatment of fast electrons. We find a clear He I {\lambda} 10830 feature which is strongest in the first few days after explosion and becomes weaker with time. Initially this feature is blended with the Mg II {\lambda} 10927 feature but over time separates to form a secondary feature to the blue wing of the Mg II {\lambda} 10927 feature. We compare our simulation to observations of iPTF13ebh, which showed a similar feature to the blue wing of the Mg II {\lambda} 10927 feature, previously identified as C I. Our simulation shows a good match to the evolution of this feature and we identify it as high velocity He I {\lambda} 10830. This suggests that He I {\lambda} 10830 could be a signature of the double detonation scenario.

Authors:Madeline Howell, Simon W. Campbell, Dennis Stello, Gayandhi M. De Silva

Abstract: Asteroseismology provides a new avenue for accurately measuring the masses of evolved globular cluster (GC) stars through the detection of their solar-like oscillations. We present the first detections of solar-like oscillations in 47 red giant branch (RGB) and early asymptotic giant branch (EAGB) stars in the metal-poor GC M80; only the second ever with measured seismic masses. We investigate two major areas of stellar evolution and GC science; the multiple populations and stellar mass-loss. We detected a distinct bimodality in the EAGB mass distribution. We showed that this is likely due to sub-population membership. If confirmed, it would be the first direct measurement of a mass difference between sub-populations. A mass difference was not detected between the sub-populations in our RGB sample. We instead measured an average RGB mass of $0.782\pm0.009~\msun$, which we interpret as the average between the sub-populations. Differing mass-loss rates on the RGB has been proposed as the second parameter that could explain the horizontal branch (HB) morphology variations between GCs. We calculated an integrated RGB mass-loss separately for each sub-population: $0.12\pm0.02~\msun$ (SP1) and $0.25\pm0.02~\msun$ (SP2). Thus, SP2 stars have greatly enhanced mass-loss on the RGB. Mass-loss is thought to scale with metallicity, which we confirm by comparing our results to a higher metallicity GC, M4. We also find that M80 stars have insignificant mass-loss on the HB. This is different to M4, suggesting that there is a metallicity and temperature dependence in the HB mass-loss. Finally, our study shows the robustness of the $\Delta\nu$-independent mass scaling relation in the low-metallicity (and low-surface gravity) regime.

Authors:Avijeet Prasad, Sanjay Kumar, Alphonse C. Sterling, Ronald L. Moore, Guillaume Aulanier, R. Bhattacharyya, Qiang Hu

Abstract: Erupting magnetic flux ropes (MFRs) play a crucial role in producing solar flares. However, the formation of erupting MFRs in complex coronal magnetic configurations and their subsequent evolution in the flaring events are not fully understood. We performed an MHD simulation of active region NOAA 12241 to understand the formation of a rising MFR during the onset of an M6.9 flare on 2014 December 18, around 21:41 UT. The MHD simulation was initialised with an extrapolated non-force-free magnetic field generated from the photospheric vector magnetogram of the active region taken a few minutes before the flare. The initial magnetic field topology displays a pre-existing sheared arcade enveloping the polarity inversion line. The simulated dynamics exhibit the movement of the oppositely directed legs of the sheared arcade field lines towards each other due to the converging Lorentz force, resulting in the onset of tether-cutting magnetic reconnection that produces an underlying flare arcade and flare ribbons. Concurrently, an MFR above the flare arcade develops inside the sheared arcade and shows a rising motion. The MFR is found to be formed in a torus-unstable region, thereby explaining its eruptive nature. Interestingly, the location and rise of the rope are in good agreement with the corresponding observations seen in EUV channels. Furthermore, the foot points of the simulation's flare arcade match well with the location of the observed parallel ribbons of the flare. The presented simulation supports the development of the MFR by the tether-cutting magnetic reconnection inside the sheared coronal arcade during flare onset. The MFR is then found to extend along the polarity inversion line (PIL) through slip-running reconnection. The MFR's eruptive nature is ascribed both to its formation in the torus-unstable region and also to the runaway tether-cutting reconnection.

Authors:C. Guillermo Giménez de Castro

Abstract: The solar chromosphere has historically been studied from spectral lines in the visible and UV, notably H{\alpha}, Ca ii, Mg ii and Ly{\alpha}. Observations at long UV wavelengths (304, 1600 and 1700 {\AA}) from space have been recently added. However, the chromosphere can also be studied in the infrared (IR), both in the continuum as in the lines. Studies in this spectral band, which by definition extends from 1 {\mu}m to 1 mm, are scarce and recent, and its advantages having been little explored. In this work we present a review of what has been done and detail how much can be done with ground-based instruments. Argentina has a set of unique telescopes for the observation of the chromosphere, some with more than 20 years of operation and in process of renovation, others recently installed and still some in development. The panorama is very encouraging and allows to anticipate a strong international cooperation with other ground and space facilities.

Authors:Zheng Sun, Ting Li, Hui Tian, Yinjun Hou, Zhenyong Hou, Hechao Chen, Xianyong Bai, Yuanyong Deng

Abstract: Partial filament eruptions have often been observed, however, the physical mechanisms that lead to filament splitting are not yet fully understood. In this study, we present a unique event of a partial filament eruption that undergoes two distinct splitting processes. The first process involves vertical splitting and is accompanied by brightenings inside the filament, which may result from internal magentic reconnection within the filament. Following the first splitting process, the filament is separated into an upper part and a lower part. Subsequently, the upper part undergoes a second splitting, which is accompanied by a coronal blowout jet. An extrapolation of the coronal magnetic field reveals a hyperbolic flux tube structure above the filament, indicating the occurrence of breakout reconnection that reduces the constraning field above. Consequently, the filament is lifted up, but at a nonuniform speed. The high-speed part reaches the breakout current sheet to generate the blowout jet, while the low-speed part falls back to the solar surface, resulting in the second splitting. In addition, continuous brightenings are observed along the flare ribbons, suggesting the occurrence of slipping reconnection process. This study presents, for the first time, the unambiguous observation of a two-stage filament splitting process, advancing our understanding of the complex dynamics of solar eruptions.

Authors:Sanjay Kumar, Avijeet Prasad, Sushree S. Nayak, Satyam Agarwal, R. Bhattacharyya

Abstract: Magnetic flux ropes (MFRs) play an important role in high-energetic events like solar flares and coronal mass ejections in the solar atmosphere. Importantly, solar observations suggest an association of some flaring events with quadrupolar magnetic configurations. However, the formation and subsequent evolution of MFRs in such magnetic configurations still need to be fully understood. In this paper, we present idealized magnetohydrodynamics (MHD) simulations of MFR formation in a quadrupolar magnetic configuration. A suitable initial magnetic field having a quadrupolar configuration is constructed by modifying a three-dimensional (3D) linear force-free magnetic field. The initial magnetic field contains neutral lines, which consist of X-type null points. The simulated dynamics initially demonstrate the oppositely directed magnetic field lines located across the polarity inversion lines (PILs) moving towards each other, resulting in magnetic reconnections. Due to these reconnections, four highly twisted MFRs form over the PILs. With time, the foot points of the MFRs move towards the X-type neutral lines and reconnect, generating complex magnetic structures around the neutral lines, thus making the MFR topology more complex in the quadrupolar configuration than those formed in bipolar loop systems. Further evolution reveals the non-uniform rise of the MFRs. Importantly, the simulations indicate that the pre-existing X-type null points in magnetic configurations can be crucial to the evolution of the MFRs and may lead to the observed brightenings during the onset of some flaring events in the quadrupolar configurations.

Authors:Mariko Kato, Izumi Hachisu, Hideyuki Saio

Abstract: We propose a helium nova model for the Large Magellanic Cloud (LMC) supersoft X-ray source (SSS) [HP99]159. This object has long been detected as a faint and persistent SSS for about 30 years, and recently been interpreted to be a source of steady helium-shell burning, because no hydrogen lines are observed. We find that the object can also be interpreted as in a decaying phase of a helium nova. The helium nova is slowly decaying toward the quiescent phase, during which the observed temperature, luminosity, and SSS lifetime ($\gtrsim 30$ years) are consistent with a massive white dwarf model of $\sim$ 1.2 $M_\odot$. If it is the case, this is the second discovery of a helium nova outburst after V445 Pup in our Galaxy and also the first identified helium nova in the LMC. We also discuss the nature of the companion helium star in relation to Type Ia supernova progenitors.

Authors:Qing-Zheng Li, Yang Huang, Xiao-Bo Dong

Abstract: We present an updated catalog of 46,753 radial velocity (RV) standard stars selected from the APOGEE DR17. These stars cover the Northern and Southern Hemispheres almost evenly, with 62% being red giants and 38% being main-sequence stars. These RV standard stars are stable on a baseline longer than 200 days (54% longer than one year and 10% longer than five years) with a median stability better than 215 m s$^{-1}$. The average observation number of those stars are 5 and each observation is required to have spectral-to-noise-ratio (SNR) greater than 50 and RV measurement error smaller than 500 m s$^{-1}$. Based on the new APOGEE RV standard star catalog, we have checked the RV zero points (RVZPs) for current large-scale stellar spectroscopic surveys including RAVE, LAMOST, GALAH and Gaia. By carefully analysis, we estimate their mean RVZP to be $+0.149$ km s$^{-1}$, $+4.574$ km s$^{-1}$ (for LRS), $-0.031$ km s$^{-1}$ and $+0.014$ km s$^{-1}$, respectively, for the four surveys. In the RAVE, LAMOST (for MRS), GALAH and Gaia surveys, RVZP exhibits systematic trend with stellar parameters (mainly [Fe/H], $T_{\rm{eff}}$, log $g$, $G_{\rm{BP}}-G_{\rm{RP}}$ and $G_{\rm{RVS}}$). The corrections of those small but clear RVZPs are of vital importances for these massive spectroscopic surveys in various studies that require extremely high radial velocity accuracies.

Authors:Nicolas Poirier Rosseland Centre for Solar Physics - University of Oslo Institute of Theoretical Astrophysics - University of Oslo, Victor Réville Research Institute for Astrophysics and Planetology - University Toulouse III Paul Sabatier, Alexis P. Rouillard Research Institute for Astrophysics and Planetology - University Toulouse III Paul Sabatier, Athanasios Kouloumvakos The Johns Hopkins University Applied Physics Laboratory, Emeline Valette Research Institute for Astrophysics and Planetology - University Toulouse III Paul Sabatier

Abstract: We analyse the signature and origin of transient structures embedded in the slow solar wind, and observed by the Wide-Field Imager for Parker Solar Probe (WISPR) during its first 10 passages close to the Sun. WISPR provides a new in-depth vision on these structures, which have long been speculated to be a remnant of the pinch-off magnetic reconnection occurring at the tip of helmet streamers. We pursue the previous modelling works of Reville (2020b, 2022) that simulate the dynamic release of quasi-periodic density structures into the slow wind through a tearing-induced magnetic reconnection at the tip of helmet streamers. Synthetic WISPR white-light (WL) images are produced using a newly developed advanced forward modelling algorithm, that includes an adaptive grid refinement to resolve the smallest transient structures in the simulations. We analyse the aspect and properties of the simulated WL signatures in several case studies, typical of solar minimum and near-maximum configurations. Quasi-periodic density structures associated with small-scale magnetic flux ropes are formed by tearing-induced magnetic reconnection at the heliospheric current sheet and within 3-7Rs. Their appearance in WL images is greatly affected by the shape of the streamer belt and the presence of pseudo-streamers. The simulations show periodicities on the ~90-180min, ~7-10hr and ~25-50hr timescales, which are compatible with WISPR and past observations. This work shows strong evidence for a tearing-induced magnetic reconnection contributing to the long-observed high variability of the slow solar wind.

Authors:Yixiao Zhou, Anish M. Amarsi, Victor Aguirre Børsen-Koch, Klara G. Karlsmose, Remo Collet, Thomas Nordlander

Abstract: Three-dimensional radiation-hydrodynamics (3D RHD) simulations of stellar surface convection provide valuable insights into many problems in solar and stellar physics. However, almost all 3D near-surface convection simulations to date are based on solar-scaled chemical compositions, which limit their application on stars with peculiar abundance patterns. To overcome this difficulty, we implement the robust and widely-used FreeEOS equation of state and our Blue opacity package into the Stagger 3D radiation-magnetohydrodynamics code. We present a new 3D RHD model of the solar atmosphere, and demonstrate that the mean stratification as well as the distributions of key physical quantities are in good agreement with those of the latest Stagger solar model atmosphere. The new model is further validated by comparing against solar observations. The new model atmospheres reproduce the observed flux spectrum, continuum centre-to-limb variation, and hydrogen line profiles at a satisfactory level, thereby confirming the realism of the model and the underlying input physics. These implementations open the prospect for studying other stars with different $\alpha$-element abundance, carbon-enhanced metal-poor stars and population II stars with peculiar chemical compositions using 3D Stagger model atmospheres.

Authors:Matheus Bernini-Peron, Wagner L. F. Marcolino, Andreas A. C. Sander, Jean-Claude Bouret, Varsha Ramachandran, Julian Saling, Fabian R. N. Schneider, Lidia M. Oskinova, Francisco Najarro

Abstract: B supergiants (BSGs) are evolved stars with effective temperatures between 10 to 30 kK and are important to understand massive star evolution. Located on the edge of the line-driven wind regime, the study of their atmospheres is helpful to understand phenomena such as the bi-stability jump. Key UV features of their spectra have so far not been reproduced by models for types later than B1. Here, we aim to remedy this situation via spectral analysis that accounts for wind clumping and X-rays. In addition, we investigate the evolutionary status of our sample stars based on the obtained stellar parameters. We determined parameters via quantitative spectroscopy using CMFGEN and PoWR codes. The models were compared to UV and optical data of four BSGs: HD206165, HD198478, HD53138, and HD164353. We also study the evolutionary status of our sample using GENEC and MESA tracks. When including clumping and X-rays, we find good agreements between synthetic and observed spectra for our sample stars. For the first time, we reproduced key lines in the UV. For that, we require a moderately clumped wind (f_infty > ~0.5). We also infer relative X-ray luminosities of ~10^-7.5 to 10^-8 -- lower than the typical ratio of 10^-7. Moreover, we find a possible mismatch between evolutionary and spectroscopic masses, which could be related to the mass-discrepancy problem present in other OB stars. Our results provide evidence that X-rays and clumping are needed to describe the winds of cool BSGs. However, their winds seem less structured than in earlier type stars. This aligns with observational X-rays and clumping constraints as well as recent hydrodynamical simulations. The BSGs' evolutionary status appears diverse: some objects are potentially post-red supergiants or merger products. The wind parameters provide evidence for a moderate mass-loss rate increase around the bi-stability jump. Abstract abridged

Authors:Shah Mohammad Bahauddin, Mark Peter Rast

Abstract: In this paper we refine a previously developed acoustic-source filter (Bahauddin & Rast 2021), improving its reliability and extending its capabilities. We demonstrate how to fine-tune the filter to meet observational constraints and to focus on specific wavefront speeds. This refinement enables discrimination of acoustic-source depths and tracking of local-source wavefronts, thereby facilitating ultra-local helioseismology on very small scales. By utilizing the photospheric Doppler signal from a subsurface source in a MURaM simulation, we demonstrate that robust ultra-local three-dimensional helioseismic inversions for the granular flows and sound speed to depths of at least 80 km below the photosphere are possible. The capabilities of the National Science Foundation's new Daniel K. Inouye Solar Telescope (DKIST) will enable such measurements of the real Sun.

Authors:N. Shagatova, A. Skopal, E. Kundra, R. Komžík, S. Yu. Shugarov, T. Pribulla, V. Krushevska

Abstract: Context. Non-dusty late-type giants without a corona and large-scale pulsations represent objects that do not fulfil the conditions under which standard mass-loss mechanisms can be applied efficiently. The driving mechanism of their winds is still unknown. Aims. The main goal of this work is to match the radial velocities of absorbing matter with a depth in the red giant (RG) atmosphere in the S-type symbiotic star EG And. Methods. We measured fluxes and radial velocities of ten FeI absorption lines from spectroscopic observations with a resolution of ~30 000. At selected orbital phases, we modelled their broadened profiles, including all significant broadening mechanisms. Results. The selected FeI absorption lines at 5151 - 6469A, originate at a radial distance ~1.03 RG radii from its centre. The corresponding radial velocity is typically ~1 km/s , which represents a few percent of the terminal velocity of the RG wind. The high scatter of the radial velocities of several km/s in the narrow layer of the stellar atmosphere points to the complex nature of the near-surface wind mass flow. The average rotational velocity of 11 km/s implies that the rotation of the donor star can contribute to observed focusing the wind towards the orbital plane. The orbital variability of the absorbed flux indicates the highest column densities of the wind in the area between the binary components, even though the absorbing neutral material is geometrically more extended from the opposite side of the giant. This wind density asymmetry in the orbital plane region can be ascribed to gravitational focusing by the white dwarf companion. Conclusions. Our results suggest that both gravitational and rotational focusing contribute to the observed enhancement of the RG wind towards the orbital plane, which makes mass transfer by the stellar wind highly efficient.

Authors:Mikhail Kovalev, Olivier R. Hainaut, Xuefei Chen, Zhanwen Han

Abstract: We present the detection of false positive double-lined spectroscopic binaries candidates (SB2) using medium-resolution survey (MRS) spectra from the one time-domain field of LAMOST data release 10 (DR10). The secondary component in all these binaries has near zero radial velocity and solar-like spectral lines. Highly likely this is light from the semi-transparent clouds illuminated by the full Moon. However we also suspect that partially this contamination can be caused by a solar light reflected from the surface of low-orbital artificial satellites launched in the beginning of 2022. We found several possible contaminant candidates using archival orbital data. We propose measures to reduce risk of such contamination for the future observations and methods to find it in archived ones.

Authors:L. Mashonkina, Yu. Pakhomov, T. Sitnova, A. Smogorzhevskii, P. Jablonka, V. Hill

Abstract: Detailed chemical abundances of very metal-poor (VMP, [Fe/H] < -2) stars are important for better understanding the First Stars, early star formation and chemical enrichment of galaxies. Big on-going and coming high-resolution spectroscopic surveys provide a wealth of material that needs to be carefully analysed. For VMP stars, their elemental abundances should be derived based on the non-local thermodynamic equilibrium (non-LTE = NLTE) line formation because low metal abundances and low electron number density in the atmosphere produce the physical conditions favorable for the departures from LTE. The galactic archaeology research requires homogeneous determinations of chemical abundances. For this purpose, we present grids of the 1D-NLTE abundance corrections for the Na I, Mg I, Ca I, Ca II, Ti II, Fe I, Zn I, Zn II, Sr II, and Ba II lines, which are used in the galactic archaeology research. The range of atmospheric parameters represents VMP stars on various evolutionary stages and covers effective temperatures from 4000 to 6500~K, surface gravities from log g = 0.5 to log g = 5.0, and metallicities $-5.0 \le$ [Fe/H] $\le -2.0$. The data is publicly available, and we provide the tools for interpolating in the grids online.

Authors:David Hendriks, Robert Izzard

Abstract: Mass-transfer interactions in binary stars can lead to accretion disk formation, mass loss from the system and spin-up of the accretor. To determine the trajectory of the mass-transfer stream, and whether it directly impacts the accretor, or forms an accretion disk, requires numerical simulations. The mass-transfer stream is approximately ballistic, and analytic approximations based on such trajectories are used in many binary population synthesis codes as well as in detailed stellar evolution codes. We use binary population synthesis to explore the conditions under which mass transfer takes place. We then solve the reduced three-body equations to compute the trajectory of a particle in the stream for systems with varying system mass ratio, donor synchronicity and initial stream velocity. Our results show that on average both more mass and more time is spent during mass transfer from a sub-synchronous donor than from a synchronous donor. Moreover, we find that at low initial stream velocity the asynchronous rotation of the donor leads to self-accretion over a large range of mass ratios, especially for super-synchronous donors. The stream (self-)intersects in a narrow region of parameter space where it transitions between accreting onto the donor or the accretor. Increasing the initial stream velocity leads to larger areas of the parameter space where the stream accretes onto the accretor, but also more (self-)intersection. The radii of closest approach generally increase, but the range of specific angular momenta that these trajectories carry at the radius of closest approach gets broader. Our results are made publicly available.

Authors:Judy Chebly, Julián D. Alvarado-Gómez, Katja Poppenhäger, Cecilia Garraffo

Abstract: As a cool star evolves, it loses mass and angular momentum due to magnetized stellar winds which affect its rotational evolution. This change has consequences that range from the alteration of its activity to influences over the atmosphere of any orbiting planet. Despite their importance, observations constraining the properties of stellar winds in cool stars are extremely limited. Therefore, numerical simulations provide a valuable way to understand the structure and properties of these winds. In this work, we simulate the magnetized winds of 21 cool main-sequence stars (F-type to M-dwarfs), using a state-of-the-art 3D MHD code driven by observed large-scale magnetic field distributions. We perform a qualitative and quantitative characterization of our solutions, analyzing the dependencies between the driving conditions (e.g., spectral type, rotation, magnetic field strength) and the resulting stellar wind parameters (e.g., Alfv\'en surface size, mass loss rate, angular momentum loss rate, stellar wind speeds). We compare our models with the current observational knowledge on stellar winds in cool stars and explore the behaviour of the mass loss rate as a function of the Rossby number. Furthermore, our 3D models encompass the entire classical Habitable Zones (HZ) of all the stars in our sample. This allows us to provide the stellar wind dynamic pressure at both edges of the HZ and analyze the variations of this parameter across spectral type and orbital inclination. The results here presented could serve to inform future studies of stellar wind-magnetosphere interactions and stellar wind erosion of planetary atmospheres via ion escape processe.

Authors:J. R. McIntyre, C. H. K. Chen, A. Larosa

Abstract: Using data from orbits one to eleven of the Parker Solar Probe (PSP) mission, the magnetic field spectral index was measured across a range of heliocentric distances. The previously observed transition between a value of $-5/3$ far from the Sun and a value of $-3/2$ close to the Sun was recovered, with the transition occurring at around $50 \, R_{\odot}$ and the index saturating at $-3/2$ as the Sun is approached. A statistical analysis was performed to separate the variation of the index on distance from its dependence on other parameters of the solar wind that are plausibly responsible for the transition; including the cross helicity, residual energy, turbulence age and the magnitude of magnetic fluctuations. Of all parameters considered the cross helicity was found to be by far the strongest candidate for the underlying variable responsible. The velocity spectral index was also measured and found to be consistent with $-3/2$ over the range of values of cross helicity measured. Possible explanations for the behaviour of the indices are discussed, including the theorised different behaviour of imbalanced, compared to balanced, turbulence.

Authors:Yingxiang Wang, Tanda Li, Shaolan Bi, Timothy R. Bedding, Yaguang Li

Abstract: This paper reports estimated stellar parameters of 1,153 Kepler red giant branch stars determined with asteroseismic modeling. We use radial-mode oscillation frequencies, gravity-mode period spacings, Gaia luminosities, and spectroscopic data to characterize these stars. Compared with previous studies, we find that the two additional observed constraints, i.e., the gravity-mode period spacing and luminosity, significantly improve the precision of fundamental stellar parameters. The typical uncertainties are 2.9% for the mass, 11% for the age, 1.0% for the radius, 0.0039 dex for the surface gravity, and 0.5\% for the helium core mass, making this the best-characterized large sample of red-giant stars available to date. With better characterizations for these red giants, we recalibrate the seismic scaling relations and study the surface term on the red-giant branch. We confirm that the surface term depends on the surface gravity and effective temperature, but there is no significant correlation with metallicity.

Authors:Suhail Masda, Z. T. Yousef, Mashhoor Al-Wardat, Awni Al-Khasawneh

Abstract: We present the detailed fundamental stellar parameters of the close visual binary system; HD39438 for the first time. We used Al-Wardat's method for analyzing binary and multiple stellar systems (BMSSs). The method implements Kurucz's plane parallel model atmospheres to construct synthetic spectral energy distributions for both components of the system. It then combines the results of the spectroscopic analysis with the photometric analysis and then compares them with the observed ones to construct the best synthetic spectral energy distributions for the combined system. The analysis gives the precise fundamental parameters of the individual components of the system. Based on the positions of the components of HD39438 on the H-R diagram, and evolutionary and isochrones tracks, we found that the system belongs to the main sequence stars with masses of 1.24 and 0.98 solar masses for the components A and B, respectively, and age of 1.995 Gyr for both components. The main result of HD39438 is new dynamical parallax, which is estimated to be 16.689+- 0.03 mas.

Authors:David Boyd

Abstract: SW Sex stars are an informal sub-class of eclipsing nova-like cataclysmic variables. We report 934 new eclipse times measured over the past 17 years for HS 0728+6738 (V482 Cam), SW Sex, DW UMa, HS 0129+2933 (TT Tri), V1315 Aql, PX And, HS 0455+8315, HS 0220+0603, BP Lyn, BH Lyn, LX Ser, UU Aqr, V1776 Cyg, RW Tri, 1RXS J064434.5+334451, AC Cnc, V363 Aur, and BT Mon. When combined with published eclipse times going back in some cases many decades, we show that these binary systems exhibit a range of behaviors, including increasing, decreasing, and possibly oscillating orbital periods. Nevertheless, the duration of these observations is still not long enough to be able to make reliable quantitative statements about their long term behaviors. In addition to these long term trends, we also observed rapid and unusual decreases in the orbital periods of SW Sex and RW Tri during 2017 and 2018, respectively.

Authors:Wangjunting Xue, Jia-Shu Niu, Hui-Fang Xue, Sijing Yin

Abstract: In this work, the pulsation analysis is performed on 83 high-amplitude $\delta$ Scuti stars, which have been observed by the Transiting Exoplanet Survey Satellite (TESS). The results show that 49 of these HADS show single-mode pulsation, 27 of them show radial double-modes pulsation (in which 22 of them pulsate with the fundamental and first overtone modes and 5 of them pulsate with the first and second overtone modes), and 7 of them show radial triple-modes pulsation (3 of which are newly confirmed triple-mode HADS). The histogram of the fundamental periods and the ratios between the fundamental and first overtone periods show bimodal structures, which might be caused by the stellar evolution in this specific phase. Most of the radial triple-mode HADS have a fundamental amplitude of 41-54 mmag, and 50% of them have similar amplitudes of the fundamental and first overtone pulsation modes. All these hints require further confirmation not only in observations with more HADS samples, but also in theoretical models with suitable treatments of stellar evolution and pulsation.

Authors:Nicole Reindl, Ramazan Islami, Klaus Werner, S. O. Kepler, Max Pritzkuleit, Harry Dawson, Matti Dorsch, Alina Istrate, Ingrid Pelisoli, Stephan Geier, Murat Uzundag, Judith Provencal, Stephen Justham

Abstract: We report on the spectroscopic confirmation of 68 new bright ($G=13.5-17.2$ mag) and blue (pre-)white dwarfs (WDs). This finding has allowed us to almost double the number of the hottest ($T_{\mathrm{eff}} \geq 60$kK) known WDs brighter than $G=16$ mag. We increased the number of known ultra-high excitation (UHE) WDs by 20%, found one unambiguous close binary system consisting of one DA WD with an irradiated low-mass companion, one DAO, and one DOA WD that are likely in their transformation phase of becoming pure DA WDs, one rare, naked O(H) star, two DA and two DAO WDs with $T_{\mathrm{eff}}$ possibly in excess of 100kK, three new DOZ WDs, and three of our targets are central stars of (possible) planetary nebulae. Using non-local thermodynamic equilibrium models, we derived the atmospheric parameters of these stars and by fitting their spectral energy distribution we derived their radii, luminosities, and gravity masses. In addition, we derived their masses in the Kiel and Hertzsprung-Russell diagram (HRD). We find that Kiel, HRD, and gravity mass agree only in half of the cases. This is not unexpected and we attribute this to the neglect of metal opacities, possibly stratified atmospheres, as well as possible uncertainties of the parallax zero point determination. Furthermore, we carried out a search for photometric variability in our targets using archival data, finding that 26% of our targets are variable. This includes 15 new variable stars, with only one of them being clearly an irradiation effect system. Strikingly, the majority of the variable stars exhibit non-sinusoidal light-curve shapes, which are unlikely explained in terms of close binary systems. We propose that a significant fraction of all (not just UHE) WDs develop spots when entering the WD cooling phase. We suggest that this could be related to the on-set of weak magnetic fields and possibly diffusion.

Authors:Kevin France, Nicole Arulanantham, Erin Maloney, P. Wilson Cauley, P. Abraham, Juan M. Alcala, Justyn Campbell-White, Eleonora Fiorellino, Gregory J. Herczeg, Brunella Nisini, Miguel Vioque

Abstract: The spatial distribution and evolution of gas in the inner 10 au of protoplanetary disks form the basis for estimating the initial conditions of planet formation. Among the most important constraints derived from spectroscopic observations of the inner disk are the radial distributions of the major gas phase constituents, how the properties of the gas change with inner disk dust evolution, and how chemical abundances and excitation conditions are influenced by the high-energy radiation from the central star. We present a survey of the radial distribution, excitation, and evolution of inner disk molecular hydrogen (H$_{2}$) obtained as part of the $HST$/ULLYSES program. We analyze far-ultraviolet spectroscopy of 71 (63 accreting) pre-main sequence systems in the ULLYSES DR5 release to characterize the H$_{2}$ emission lines, H$_{2}$ dissociation continuum emission, and major photochemical/disk evolution driving UV emissions (Ly$\alpha$, UV continuum, and C IV). We use the widths of the H$_{2}$ emission lines to show that most fluorescent H$_{2}$ arises between 0.1 - 1.4 au from the parent star, and show positive correlations of the average emitting radius with the accretion luminosity and with the dust disk mass. We find a strong correlation between H$_{2}$ dissociation emission and both the accretion-dominated Ly$\alpha$ luminosity and the inner disk dust clearing, painting a picture where water molecules in the inner 3 au are exposed to and dissociated by strong Ly$\alpha$ emission as the opacity of the inner disk declines with time.

Authors:Ilaria Pascucci, Bennett N. Skinner, Dingshan Deng, Maxime Ruaud, Uma Gorti, Kamber R. Schwarz, Edwige Chapillon, Miguel Vioque, James Miley

Abstract: We present an ACA search for [CI] emission at 492GHz toward large T Tauri disks (gas radii $\gtrsim 200$au) in the $\sim 1-3$Myr-old Lupus star-forming region. Combined with ALMA 12-m archival data for IM Lup, we report [CI] detections in 6 out of 10 sources, thus doubling the known detections toward T Tauri disks. We also identify four Keplerian double-peaked profiles and demonstrate that [CI] fluxes correlate with $^{13}$CO, C$^{18}$O, and $^{12}$CO(2-1) fluxes, as well as with the gas disk outer radius measured from the latter transition. These findings are in line with the expectation that atomic carbon traces the disk surface. In addition, we compare the carbon and CO line luminosities of the Lupus and literature sample with [CI] detections with predictions from the self-consistent disk thermo-chemical models of Ruaud et al. (2022). These models adopt ISM carbon and oxygen elemental abundances as input parameters. With the exception of the disk around Sz 98, we find that these models reproduce all available line luminosities and upper limits with gas masses comparable to or higher than the minimum mass solar nebula and gas-to-dust mass ratios $\geq 10$. Thus, we conclude that the majority of large Myr-old disks conform to the simple expectation that they are not significantly depleted in gas, CO, or carbon.

Authors:Jian-Ying Bai, Jing Wang, Hua-Li Li, Li-Ping Xin, Guang-Wei Li, Yuan-Gui Yang, Jian-Yan Wei

Abstract: We observed active M dwarf star AD Leo for 146 hr in photometry by GWAC-F30 and also analyzed 528-hr photometric data of the star from TESS. A total of 9 and 70 flares are detected from GWAC-F30 and TESS, respectively. Flare durations, amplitudes and energies are calculated. The distributions of the three properties and FFDs are given. Within the same energy range of flares, the FFDs of AD Leo obtained in this research and the previous study are basically consistent, which suggests that the magnetic activity of this star has not significantly changed compared to that decades ago. Comparing with the average FFD of M-type stars, AD Leo's FFD is twice higher, indicating that its magnetic activity is more active than that of the average level of the M-type. Based on TESS light curve, AD Leo's rotation period is calculated as 2.21${+0.01 \choose -0.01}$ day , supporting the result given in previous research. During the decay phase of the most energetic flare from TESS, we identified QPPs and determined a 26.5-min oscillation period, which is currently the longest period for AD Leo, suggesting that long periodic physical process existed during flare of this star.

Authors:S. Nidhi, Blesson Mathew, B. Shridharan, R. Arun, R. Anusha, Sreeja S. Kartha

Abstract: We study a sample of 119 Herbig Ae/Be stars in the Galactic anti-center direction using the spectroscopic data from Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) survey program. Emission lines of hydrogen belonging to the Balmer and Paschen series, and metallic lines of species such as FeII, OI, CaII triplet are identified. A moderate correlation is observed between the emission strengths of H$\alpha$ and FeII 5169 \r{A}, suggesting a possible common emission region for FeII lines and one of the components of H$\alpha$. We explored a technique for the extinction correction of the HAeBe stars using diffuse interstellar bands present in the spectrum. We estimated the stellar parameters such as age and mass of these HAeBe stars, which are found to be in the range 0.1 -- 10 Myr and 1.5 -- 10 $M_{\odot}$, respectively. We found that the mass accretion rate of the HAeBe stars in the Galactic anti-center direction follows the relation $\dot{M}_{acc}$ $\propto$ $M_{*}^{3.12^{+0.21}_{-0.34}}$, which is similar to the relation derived for HAeBe stars in other regions of the Galaxy. The mass accretion rate of HAeBe stars is found to have a functional form of $\dot{M}_{acc} \propto t^{-1.1 \pm 0.2}$ with age, in agreement with previous studies.

Authors:Vladimir Dorovskyy, Valentin Melnik, Anatolii Brazhenko

Abstract: The purpose of this work is to demonstrate the effectiveness of ground-based support for space missions, primarily PSP, using large Ukrainian decameter radio telescopes. Another goal of the work is to carry out cross calibration of the radiometers onboard spacecraft using the calibrated data of the ground-based radio telescopes. One of the most common methods of remote diagnostics of the solar corona is the study of radio emission, the sources of which are located in the solar corona at different heliocentric altitudes. The technique of joint space terrestrial observations consists in the simultaneous observation of individual events and their analysis in the widest possible frequency band during the maximum approach of the PSP vehicle to the Sun. At the same time, observation in the common frequency band is proposed to be used for calibration of the onboard radio receivers. The methods of planning joint space terrestrial observations are substantiated. Using the data of the UTR 2, URAN 2 radio telescopes and the PSP probe, the dynamic and polarization spectra of the simultaneously observed bursts on June 9, 2020 were obtained. The identification and comparison of individual bursts was carried out. A common dynamic spectrum of the bursts in the frequency band 0.5 ... 32 MHz was obtained. Cross calibration of the HFR receiver of the FIELDS PSP module in the frequency band 10...18 MHz was made using the calibrated data of terrestrial radio telescopes. The effectiveness of ground-based support of the PSP mission by the large Ukrainian radio telescopes is shown. Examples of joint observations are given, and the method of cross calibration of the FIELD PSP module receivers is demonstrated. Prospects for further ground based support for solar space missions are presented

Authors:Peter Foukal

Abstract: The area ratios of sunspots to white light faculae in the first two years of sunspot cycles 12-21 correlate remarkably well with the peak amplitudes of those cycles between 1878-1980 (Brown and Evans, 1980). This finding could not be used to predict subsequent cycle amplitudes because the Royal Greenwich Observatory program of facular area measurements was discontinued in 1976. We use continuum images from the Michelson Doppler Imager (MDI) and the Heliospheric and Magnetic Imager (HMI) to show that the close relation holds also for cycle 24, and we predict an amplitude of approximately 185 for the current cycle 25.

Authors:Abhay Pratap Yadav, Sugyan Parida, Yogesh Chandra Joshi, Santosh Joshi

Abstract: Luminous blue variables (LBVs) are evolved massive stars close to the Eddington limit, with a distinct spectroscopic and photometric variability having unsteady mass-loss rates. These stars show a considerable change in their surface temperature from quiescent to outbursts phase. The cause of irregular variability and unsteady mass-loss rate is not properly understood. Here we present the result of linear stability analysis in two LBVs AF And and R 127 during their quiescent and outburst phase. We note that several modes are unstable in the models of the considered LBVs. Mode interaction is frequent in the modal diagrams for the models of both LBVs. For AF And, number of instabilities increase in models having temperature below 15000 K. The found instabilities may be linked with the observed irregular variabilities and surface eruptions. Observational facilities of Belgo-Indian Network for Astronomy and Astrophysics (BINA) will be very beneficial to study the spectroscopic and photometric behavior of the considered LBVs.

Authors:Muthu Priyal, Jagdev Singh, B. Raghavendra Prasad, Chavali Sumana, Varun Kumar, Shalabh Mishra, S. N. Venkata, G. Sindhuja, K. Sasikumar Raja, Amit Kumar, Sanal krishnan, Bhavana S. Hegde, D. Utkarsha, Natarajan Venkatasubramanian, Pawankumar Somasundram, S. Nagabhushana, PU. Kamath, S. Kathiravan, T. Vishnu Mani, Suresh Basavaraju, Rajkumar Chavan, P. Vemareddy, B. Ravindra, S. P. Rajaguru, K. Nagaraju, Wageesh Mishra, Jayant Joshi, Tanmoy Samanta, Piyali Chatterjee, C. Kathiravan, R. Ramesh

Abstract: ADITYA-L1 is India's first dedicated mission to observe the sun and its atmosphere from a halo orbit around L1 point. Visible emission line coronagraph (VELC) is the prime payload on board at Aditya-L1 to observe the sun's corona. VELC is designed as an internally occulted reflective coronagraph to meet the observational requirements of wide wavelength band and close to the solar limb (1.05 Ro). Images of the solar corona in continuum and spectra in three emission lines 5303{\AA} [Fe xiv], 7892{\AA} [Fe xi] and 10747 [Fe xiii] obtained with high cadence to be analyzed using software algorithms automatically. A reasonable part of observations will be made in synoptic mode, those, need to be analyzed and results made available for public use. The procedure involves the calibration of instrument and detectors, converting the images into fits format, correcting the images and spectra for the instrumental effects, align the images etc. Then, develop image processing algorithms to detect the occurrence of energetic events using continuum images. Also derive physical parameters, such as temperature and velocity structure of solar corona using emission line observations. Here, we describe the calibration of detectors and the development of software algorithms to detect the occurrence of CMEs and analyze the spectroscopic data.

Authors:A. V. Bobakov, A. V. Karpova, S. V. Zharikov, A. Yu. Kirichenko, Yu. A. Shibanov, D. A. Zyuzin

Abstract: We present the results of optical spectroscopy of stellar companions to three binary millisecond pulsars, PSRs J0621$+$2514, J2317$+$1439 and J2302$+$4442, obtained with the Gran Telescopio Canarias. The spectrum of the J0621$+$2514 companion shows a blue continuum and prominent Balmer absorption lines. The latter are also resolved in the spectrum of the J2317$+$1439 companion, showing that both are DA-type white dwarfs. No spectral features are detected for the J2302$+$4442 companion, however, its broadband magnitudes and the spectral shape of the continuum emission imply that this is also a DA-type white dwarf. Based on the spectral analyses, we conclude that the companions of J0621$+$2514 and J2317$+$1439 are relatively hot, with effective temperatures $T_{\rm eff}$$=$8600$\pm$200 and 9600$\pm$2000~K, respectively, while the J2302$+$4442 companion is significantly cooler, $T_{\rm eff}$$<$6000~K. We also estimated the distance to J0621$+$2514 of 1.1$\pm$0.3 kpc and argue that its companion and the companion of J2317$+$1439 are He-core white dwarfs providing constraints on their cooling ages of $\lesssim$2 Gyr.

Authors:Bahaeddine Gannouni, Victor Réville, Alexis Rouillard, Kévin Dalmasse

Abstract: We investigate the origin of mesoscale structures in the solar wind called microstreams defined as enhancements in solar wind speed and temperature that last several hours. They were first clearly detected in Helios and Ulysses solar wind data and are now omnipresent in the "young" solar wind measured by Parker Solar Probe and Solar Orbiter. These recent data reveal that microstreams transport a profusion of Alfv\'enic perturbations in the form of velocity spikes and magnetic switchbacks. In this study we use a very high-resolution 2.5 MHD model of the corona and the solar wind to simulate the emergence of magnetic bipoles interacting with the pre-existing ambient corona and the creation of jets that become microstreams propagating in the solar wind. Our high-resolution simulations reach sufficiently high Lundquist numbers to capture the tearing mode instability that develops in the reconnection region and produces plasmo\"ids released with the jet into the solar wind. Our domain runs from the lower corona to 20 Rs, this allows us to track the formation process of plasmo\"ids and their evolution into Alfv\'enic velocity spikes. We obtain perturbed solar wind flows lasting several hours with velocity spikes occurring at characteristic periodicities of about 19 minutes. We retrieve several properties of microstreams measured in the pristine solar wind by Parker Solar Probe, namely an increase in wind velocity of about 100 km/s during the streams passage together with superposed velocity spikes of also about 100 km/s released into the solar wind.

Authors:M. Janvier, S. Mzerguat, P. R. Young, É. Buchlin, A. Manou, G. Pelouze, D. M. Long, L. Green, A. Warmuth, F. Schuller, P. Démoulin, D. Calchetti, F. Kahil, L. Bellot Rubio, S. Parenti, S. Baccar, K. Barczynski, L. K. Harra, L. A. Hayes, W. T. Thompson, D. Müller, D. Baker, S. Yardley, D. Berghmans, C. Verbeeck, P. J. Smith, H. Peter, R. Aznar Cuadrado, S. Musset, D. H. Brooks, L. Rodriguez, F. Auchère, M. Carlsson, A. Fludra, D. Hassler, D. Williams, M. Caldwell, T. Fredvik, A. Giunta, T. Grundy, S. Guest, E. Kraaikamp, S. Leeks, J. Plowman, W. Schmutz, U. Schühle, S. D. Sidher, L. Teriaca, S. K. Solanki, J. C. del Toro Iniesta, J. Woch, A. Gandorfer, J. Hirzberger, D. Orozco Suarez, T. Appourchaux, G. Valori, J. Sinjan, K. Albert, R. Volkmer

Abstract: The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2/4/2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth's orbit. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. We use the observations from a multi-view dataset, which includes EUV imaging to spectroscopy and magnetic field measurements. These data come from IRIS, SDO, Hinode, as well as several instruments on Solar Orbiter. Information given by SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode/EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission.

Authors:Oana Vesa, Jason Jackiewicz, Kevin Reardon

Abstract: Atmospheric gravity waves (AGWs) are low-frequency, buoyancy-driven waves that are generated by turbulent convection and propagate obliquely throughout the solar atmosphere. Their proposed energy contribution to the lower solar atmosphere and sensitivity to atmospheric parameters (e.g. magnetic fields and radiative damping) highlight their diagnostic potential. We investigate AGWs near a quiet Sun disk center region using multi-wavelength data from the Interferometric BIdimensional Spectrometer (IBIS) and the Solar Dynamics Observatory (SDO). These observations showcase the complex wave behavior present in the entire acoustic-gravity wave spectrum. Using Fourier spectral analysis and local helioseismology techniques on simultaneously observed line core Doppler velocity and intensity fluctuations, we study both the vertical and horizontal properties of AGWs.Propagating AGWs with perpendicular group and phase velocities are detected at the expected temporal and spatial scales throughout the lower solar atmosphere. We also find previously unobserved, varied phase difference distributions among our velocity and intensity diagnostic combinations. Time-distance analysis indicates that AGWs travel with an average group speed of 4.5 kms$^{-1}$, which is only partially described by a simple simulation suggesting that high-frequency AGWs dominate the signal. Analysis of the median magnetic field (4.2 G) suggests that propagating AGWs are not significantly affected by quiet Sun photospheric magnetic fields. Our results illustrate the importance of multi-height observations and the necessity of future work to properly characterize this observed behavior.

Authors:I. Arregui, D. Y. Kolotkov, V. M. Nakariakov

Abstract: We compute the evidence in favour of two models, one based on field-aligned thermal conduction alone and another that includes thermal misbalance as well, in explaining the damping of slow magneto-acoustic waves in hot coronal loops. Our analysis is based on the computation of the marginal likelihood and the Bayes factor for the two damping models. We quantify their merit in explaining the apparent relationship between slow mode periods and damping times, measured with SOHO/SUMER in a set of hot coronal loops. The results indicate evidence in favour of the model with thermal misbalance in the majority of the sample, with a small population of loops for which thermal conduction alone is more plausible. The apparent possibility of two different regimes of slow-wave damping, if due to differences between the loops of host active regions and/or the photospheric dynamics, may help with revealing the coronal heating mechanism.

Authors:Dennis Tilipman, Maria Kazachenko, Benoit Tremblay, Ivan Milic, Valentin Martinez Pillet, Matthias Rempel

Abstract: Poynting flux is the flux of magnetic energy, which is responsible for chromospheric and coronal heating in the solar atmosphere. It is defined as a cross product of electric and magnetic fields, and in ideal MHD conditions it can be expressed in terms of magnetic field and plasma velocity. Poynting flux has been computed for active regions and plages, but estimating it in the quiet Sun (QS) remains challenging due to resolution effects and polarimetric noise. However, with upcoming DKIST capabilities, these estimates will become more feasible than ever before. Here, we study QS Poynting flux in Sunrise/IMaX observations and MURaM simulations. We explore two methods for inferring transverse velocities from observations - FLCT and a neural network based method DeepVel - and show DeepVel to be the more suitable method in the context of small-scale QS flows. We investigate the effect of azimuthal ambiguity on Poynting flux estimates, and we describe a new method for azimuth disambiguation. Finally, we use two methods for obtaining the electric field. The first method relies on idealized Ohm's law, whereas the second is a state-of-the-art inductive electric field inversion method PDFI SS. We compare the resulting Poynting flux values with theoretical estimates for chromospheric and coronal energy losses and find that some of Poynting flux estimates are sufficient to match the losses. Using MURaM simulations, we show that photospheric Poynting fluxes vary significantly with optical depth, and that there is an observational bias that results in underestimated Poynting fluxes due to unaccounted shear term contribution.

Authors:Zheyi Ding, Gang Li, Adolfo Santa Fe Dueñas, Robert W. Ebert, Nicolas Wijsen, Stefaan Poedts

Abstract: We examine the East-West asymmetry of the peak intensity in energetic storm particle (ESP) events using the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model. We find that injection efficiency peaks east of the nose of coronal mass ejection shock where the shock exhibits a quasi-parallel geometry. We show that the peak intensity at the eastern flank is generally larger than that at the western flank and it positively correlates with the injection efficiency. We also examine this asymmetry for heavy ions, which depends sensitively on the ion energy. Comparison between the modelling results with the measurements of ESP events at 1 au shows a reasonable agreement. We suggest that the injection efficiency can be a primary factor leading to the East-West asymmetry of the peak intensity in ESP events. Additionally, the charge-to-mass (Q/A) dependence of the maximum particle energy affects this asymmetry for heavy ions.

Authors:J. Farihi, J. J. Hermes, S. P. Littlefair, I. D. Howarth, N. Walters, S. G. Parsons

Abstract: This paper reports the ULTRACAM discovery of dipolar surface spots in two cool magnetic white dwarfs with Balmer emission lines, while a third system exhibits a single spot, similar to the prototype GD 356. The light curves are modeled with simple, circular, isothermal dark spots, yielding relatively large regions with minimum angular radii of 20 deg. For those stars with two light curve minima, the dual spots are likely observed at high inclination (or colatitude), however, identical and antipodal spots cannot simultaneously reproduce both the distinct minima depths and the phases of the light curve maxima. The amplitudes of the multi-band photometric variability reported here are all several times larger than that observed in the prototype GD 356; nevertheless, all DAHe stars with available data appear to have light curve amplitudes that increase toward the blue in correlated ratios. This behavior is consistent with cool spots that produce higher contrasts at shorter wavelengths, with remarkably similar spectral properties given the diversity of magnetic field strengths and rotation rates. These findings support the interpretation that some magnetic white dwarfs generate intrinsic chromospheres as they cool, and that no external source is responsible for the observed temperature inversion. Spectroscopic time-series data for DAHe stars is paramount for further characterization, where it is important to obtain well-sampled data, and consider wavelength shifts, equivalent widths, and spectropolarimetry.

Authors:Giovanni M. Mirouh, David D. Hendriks, Sophie Dykes, Maxwell Moe, Robert G. Izzard

Abstract: Binary stars evolve into chemically-peculiar objects and are a major driver of the Galactic enrichment of heavy elements. During their evolution they undergo interactions, including tides, that circularize orbits and synchronize stellar spins, impacting both individual systems and stellar populations. Using Zahn's tidal theory and MESA main-sequence model grids, we derive the governing parameters $\lambda_{lm}$ and $E_2$, and implement them in the new MINT library of the stellar population code BINARY_C. Our MINT equilibrium tides are 2 to 5 times more efficient than the ubiquitous BSE prescriptions while the radiative-tide efficiency drops sharply with increasing age. We also implement precise initial distributions based on bias-corrected observations. We assess the impact of tides and initial orbital-parameter distributions on circularization and synchronization in eight open clusters, comparing synthetic populations and observations through a bootstrapping method. We find that changing the tidal prescription yields no statistically-significant improvement as both calculations typically lie within 0.5$\sigma$. The initial distribution, especially the primordial concentration of systems at $\log_{10}(P/{\rm d}) \approx 0.8, e\approx 0.05$ dominates the statistics even when artificially increasing tidal strength. This confirms the inefficiency of tides on the main sequence and shows that constraining tidal-efficiency parameters using the $e-\log_{10}(P/{\rm d})$ distribution alone is difficult or impossible. Orbital synchronization carries a more striking age-dependent signature of tidal interactions. In M35 we find twice as many synchronized rotators in our MINT calculation as with BSE. This measure of tidal efficiency is verifiable with combined measurements of orbital parameters and stellar spins.

Authors:Hideyuki Umeda, Chris Nagele

Abstract: In this paper we revisit metal-enriched pair instability supernovae (PISNe) models which undergo chemically homogeneous evolution (CHE). By calculating multiple models, we intend to clarify mass ranges for the PISNe, $^{56}$Ni masses from the PISNe, and mass loss histories of CHE-PISNe models for metallicities consistent with the Small Magellanic Cloud (SMC) and with the Large Magellanic Cloud (LMC). We show that for an initial velocity of $v_{\rm i}/ v_{\rm k}$ = 0.1, these models undergo CHE and He-rich (Type Ib) PISNe occur in a lower mass range ($M_{\rm i} \sim 110-170 M_\odot$) than for more slowly rotating models. Interestingly, bright PISNe which have $^{56}$Ni masses larger than 10 $M_\odot$ occur in a relatively small mass range, $M_{\rm i} \sim 140-170 M_\odot$. Another notable characteristic of CHE-PISNe is the large late time mass loss rates; consequently, CSM interaction may be observable in their light curves. We also show some examples of O-rich (Type Ic) CHE-PISNe produced by $v_{\rm i}/ v_{\rm k}$ = 0.2 models. We expect these models to exhibit interaction with O-rich CSM, behavior which is consistent with the observed properties of the recently discovered PISN candidate, SN2018ibb. Finally, we present a collapsing $v_{\rm i}/ v_{\rm k}$ = 0.2 model which has sufficient angular momentum to be regarded as a candidate for a Super-Kilonova.

Authors:Thomas N. Woods, Bennet Schwab, Robert Sewell, Anant Kumar Telikicherla Kandala, James Paul Mason, Amir Caspi, Thomas Eden, Amal Chandran, Phillip C. Chamberlin, Andrew R. Jones, Richard Kohnert, Christopher S. Moore, Stanley C. Solomon, Harry Warren

Abstract: Three generations of the Miniature X-ray Solar Spectrometer (MinXSS) have flown on small satellites with the goal "to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth's ionosphere and thermosphere". The primary science instrument is the Amptek X123 X-ray spectrometer that has improved with each generation of the MinXSS experiment. This third generation MinXSS-3 has higher energy resolution and larger effective area than its predecessors and is also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). It was launched on the INSPIRESat-1 satellite on 2022 February 14, and INSPIRESat-1 has successfully completed its 6-month prime mission. The INSPIRESat-1 is in a dawn-dusk, Sun-Synchronous Orbit (SSO) and therefore has 24-hour coverage of the Sun during most of its mission so far. The rise of Solar Cycle 25 (SC-25) has been observed by DAXSS. This paper introduces the INSPIRESat-1 DAXSS solar SXR observations, and we focus the science results here on a solar occultation experiment and multiple flares on 2022 April 24. One key flare result is that the reduction of elemental abundances is greatest during the flare impulsive phase and thus highlighting the important role of chromospheric evaporation during flares to inject warmer plasma into the coronal loops. Furthermore, these results are suggestive that the amount of chromospheric evaporation is related to flare temperature and intensity.

Authors:B. Shridharan, Blesson Mathew, R. Arun, T. B. Cysil, A. Subramaniam, P. Manoj, G. Maheswar, T. P. Sudheesh

Abstract: Early Herbig Be (HBe) stars are massive, young stars accreting through the Boundary Layer mechanism. However, given the rapid ($<$ 2 Myr) evolution of early Herbig stars to the main-sequence phase, studying the evolution of the circumstellar medium around these stars can be a cumbersome exercise. In this work, we study the sample of early (B0-B5) HBe stars using the correlation between H$\alpha$ emission strength and near--infrared excess, complemented by the analysis of various emission features in the X-Shooter spectra. We segregate the sample of 37 early HBe stars based on the median values of H$\alpha$ equivalent width (EW) and near--infrared index (n(J$-$H)) distributions. The stars with |H$\alpha$ EW| $>$ 50 {\AA} and n(J$-$H) $>$ -2 are classified as intense HBe stars and stars with |H$\alpha$ EW| $<$ 50 {\AA} and n(J$-$H) $<$ -2 as weak HBe stars. Using the VLT/X--Shooter spectra of five intense and eight weak HBe stars, we visually checked for the differences in intensity and profiles of various H{\sc I} and metallic emission lines commonly observed in Herbig stars. We propose that the intense HBe stars possess an inner disk close to the star (as apparent from the high near-infrared excess) and an active circumstellar environment (as seen from high H$\alpha$ EW value and presence of emission lines belonging to Fe{\sc II}, Ca{\sc II}, O{\sc I} and [O{\sc I}]). However, for weak HBe stars, the inner disk has cleared, and the circumstellar environment appears more evolved than for intense HBe stars. Furthermore, we compiled a sample of $\sim$58,000 emission-line stars published in \textit{Gaia DR3} to identify more intense HBe candidates. Further spectroscopic studies of these candidates will help us to understand the evolution of the inner ($\sim$a few au) disk in early HBe stars.

Authors:Qing-Min Zhang, Zhen-Yong Hou, Xian-Yong Bai

Abstract: In this paper, the well-known graduated cylindrical shell (GCS) model is slightly revised by introducing longitudinal and latitudinal deflections of prominences originating from active regions (ARs). Subsequently, it is applied to the three-dimensional (3D) reconstruction of an eruptive prominence in AR 13110, which produced an M1.7 class flare and a fast coronal mass ejection (CME) on 2022 September 23. It is revealed that the prominence undergoes acceleration from $\sim$246 to $\sim$708 km s$^{-1}$. Meanwhile, the prominence experiences southward deflection by 15$\degr$$\pm$1$\degr$ without longitudinal deflection, suggesting that the prominence erupts non-radially. Southward deflections of the prominence and associated CME are consistent, validating the results of fitting using the revised GCS model. Besides, the true speed of the CME is calculated to be 1637$\pm$15 km s$^{-1}$, which is $\sim$2.3 times higher than that of prominence. This is indicative of continuing acceleration of the prominence during which flare magnetic reconnection reaches maximum beneath the erupting prominence. Hence, the reconstruction using the revised GCS model could successfully track a prominence in its early phase of evolution, including acceleration and deflection.

Authors:S. Bellotti, J. Morin, L. T. Lehmann, C. P. Folsom, G. A. J. Hussain, P. Petit, J. F. Donati, A. Lavail, A. Carmona, E. Martioli, B. Romano Zaire, E. Alecian, C. Moutou, P. Fouque, S. Alencar, E. Artigau, I. Boisse, F. Bouchy, C. Cadieux, R. Cloutier, N. Cook, X. Delfosse, R. Doyon, G. Hebrard, O. Kochukhov, G. Wade

Abstract: One manifestation of dynamo action on the Sun is the 22-yr magnetic cycle, exhibiting a polarity reversal and a periodic conversion between poloidal and toroidal fields. For M dwarfs, several authors claim evidence of activity cycles from photometry and analyses of spectroscopic indices, but no clear polarity reversal has been identified from spectropolarimetric observations. Our aim is to monitor the evolution of the large-scale field of AD Leo, which has shown hints of a secular evolution from past dedicated spectropolarimetric campaigns. We analysed near-infrared spectropolarimetric observations of the active M dwarf AD Leo taken with SPIRou between 2019 and 2020 and archival optical data collected with ESPaDOnS and Narval between 2006 and 2019. We searched for long-term variability in the longitudinal field, the width of unpolarised Stokes profiles, the unsigned magnetic flux derived from Zeeman broadening, and the geometry of the large-scale magnetic field using both Zeeman-Doppler Imaging and Principal Component Analysis. We found evidence of a long-term evolution of the magnetic field, featuring a decrease in axisymmetry (from 99% to 60%). This is accompanied by a weakening of the longitudinal field (-300 to -50 G) and a correlated increase in the unsigned magnetic flux (2.8 to 3.6 kG). Likewise, the width of the mean profile computed with selected near-infrared lines manifests a long-term evolution corresponding to field strength changes over the full time series, but does not exhibit modulation with the stellar rotation of AD Leo in individual epochs. The large-scale magnetic field of AD Leo manifested first hints of a polarity reversal in late 2020 in the form of a substantially increased dipole obliquity, while the topology remained predominantly poloidal and dipolar. This suggests that low-mass M dwarfs with a dipole-dominated magnetic field can undergo magnetic cycles.

Authors:Scott G. Engle, Edward F. Guinan

Abstract: Age is a fundamental stellar property, yet for many stars it is difficult to reliably determine. For M dwarfs it has been notoriously so. Due to their lower masses, core hydrogen fusion proceeds at a much slower rate in M dwarfs than it does in more massive stars like the Sun. As a consequence, more customary age determination methods (e.g. isochrones and asteroseismology) are unreliable for M dwarfs. As these methods are unavailable, many have searched for reliable alternatives. M dwarfs comprise the overwhelming majority of the nearby stellar inventory, which makes the determination of their fundamental parameters even more important. Further, an ever-increasing number of exoplanets are being found to orbit M dwarfs and recent studies have suggested they may relatively higher number of low-mass planets than other spectral types. Determining the ages of M dwarfs then allows us to better study any hosted exoplanets, as well. Fortunately, M dwarfs possess magnetic activity and stellar winds like other cool dwarf stars. This causes them to undergo the spindown effect (rotate with longer periods) as they age. For this reason, stellar rotation rate has been considered a potentially powerful age determination parameter for over 50 years. Calibrating reliable age-rotation relationships for M dwarfs has been a lengthy process, but here we present the age-rotation relationships for ~M0-6.5 dwarfs, determined as part of the Living with a Red Dwarf program. These relationships should prove invaluable for a wide range of stellar astrophysics and exoplanetary science applications.

Authors:C. Ian Short

Abstract: We present Version 2023-02-04 (ISO) of the Chroma+ atmospheric, spectrum, and transit light-curve modelling suite, which incorporates the VALD atomic line list. This is a major improvement as the previous versions used the much smaller NIST line list. The NIST line list is still available in Chroma+ for those projects requiring speed over completeness of line opacity. We describe a procedure for exploiting the ''Array job'' capability of the slurm workload manager on multi-cpu machines to compute broadband high resolution spectra with the VALD line list quickly using the Java version of the code (ChromaStarServer (CSS)). The inclusion of a much larger line list more completely allows for the many weaker lines that over-blanket the blue band in late-type stars and has allowed us to reduce the amount of additional ad hoc continuous opacity needed to fit the solar spectral energy distribution (SED). The additional line opacity exposed a subtle bug in the spectrum synthesis procedure that was causing residual blue line wing opacity to accumulate at shorter wavelengths. We present our latest fits to the observed solar SED and to the observed rectified high resolution visible band spectra of the Sun and the standard stars Arcturus and Vega. We also introduce the fully automated Burke-Gaffney Observatory (BGO) at Saint Mary's University (SMU) and compare our synthetic spectra to low resolution spectra obtained with our grism spectrograph that is available to students. The fully automated BGO, the spectrograph, and the BGO spectrum reduction procedure are fully described in a companion paper. All codes are available from the OpenStars www site: www.ap.smu.ca/OpenStars.

Authors:Barnabas Barna, Andrea P. Nagy, Zsofia Bora, Donat R. Czavalinga, Reka Konyves-Toth, Tamas Szalai, Peter Szekely, Szanna Zsiros, Dominik Banhidi, Barna I. Biro, Istvan Csanyi, Levente Kriskovics, Andras Pal, Zsofia M. Szabo, Robert Szakats, Krisztian Vida, Zsofia Bodola, Jozsef Vinko

Abstract: The nearby spiral galaxy NGC 3147 hosted three Type Ia supernovae (SNe Ia) in the past decades, which have been subjects of intense follow-up observations. Simultaneous analysis of their data provides a unique opportunity for testing the different light curve fitting methods and distance estimations. The detailed optical follow-up of SN 2021hpr allows us to revise the previous distance estimations to NGC 3147, and compare the widely used light curve fitting algorithms to each other. After the combination of the available and newly published data of SN 2021hpr, its physical properties can be also estimated with higher accuracy. We present and analyse new BVgriz and Swift photometry of SN 2021hpr to constrain its general physical properties. Together with its siblings, SNe 1997bq and 2008fv, we cross-compare the individual distance estimates of these three SNe given by the SALT code, and also check their consistency with the results from the MLCS2k2 method. The early spectral series of SN 2021hpr are also fit with the radiative spectral code TARDIS in order to verify the explosion properties and constrain the chemical distribution of the outer ejecta. After combining the distance estimates for the three SNe, the mean distance to their host galaxy, NGC 3127, is 42.5 $\pm$ 1.0 Mpc, which matches with the distance inferred by the most up-to-date LC fitters, SALT3 and BayeSN. We confirm that SN~2021hpr is a Branch-normal Type Ia SN that ejected $\sim 1.12 \pm 0.28$ M$_\odot$ from its progenitor white dwarf, and synthesized $\sim 0.44 \pm 0.14$ M$_\odot$ of radioactive $^{56}$Ni.

Authors:T. Felipe, S. J. González Manrique, C. R. Sangeetha, A. Asensio Ramos

Abstract: Several studies have reported magnetic field fluctuations associated with umbral shock waves. We aim to study the properties and origin of magnetic field fluctuations in the umbral chromosphere. Temporal series of spectropolarimetric observations were acquired with the GREGOR telescope. The chromospheric and photospheric conditions were derived from simultaneous inversions of the He I 10830 \AA\ triplet and the Si I 10827 \AA\ line using HAZEL2. The oscillations are interpreted using wavelet analysis and context information from UV observations acquired with SDO/AIA and IRIS. The chromospheric magnetic field shows strong fluctuations in the sunspot umbra, with peak field strengths up to 2900 G. Magnetic field and velocity umbral oscillations exhibit a strong coherence, with the magnetic field lagging the shock fronts detected in the velocity fluctuations. This points to a common origin of the fluctuations in both parameters, whereas the analysis of the phase shift between photospheric and chromospheric velocity is consistent with upwards wave propagation. These results suggest that the strong inferred magnetic field fluctuations are caused by changes in the response height of the He I 10830 \AA\ line to the magnetic field, which is sensitive to high photospheric layers after the shock fronts. The coronal activity seen in EUV data could possibly have some impact on the inferred fluctuations, but it is not the main driver of the magnetic field oscillations since they are found before EUV events take place. Chromospheric magnetic field fluctuations measured with the He I 10830 \AA\ triplet arise due to variations in the opacity of the line. After shocks produced by slow magnetoacoustic waves, the response of the line to the magnetic field can be shifted down to the upper photosphere. This is seen as remarkably large fluctuations in the line of sight magnetic field strength.

Authors:E. Paunzen, K. Bernhard, J. Budaj, F. -J. Hambsch, S. Hümmerich, D. Jones, J. Krticka

Abstract: Spectra of planetary nebulae (PNe) are characterised by strong forbidden emission lines and often also by an infrared (IR) excess. A few PNe show dust obscuration events and/or harbour long-period binaries. Some post-asymptotic giant branch stars, symbiotic stars, or B[e] stars may feature similar characteristics. Recently, dust clouds eclipsing white dwarfs were also detected. We report the discovery of an object with a very peculiar variability pattern that bears signatures compatible with the above-mentioned classes of objects. The object is ZTFJ201451.59+120353.4 and identifies with PM 1-322. The object was discovered in Zwicky Transient Facility archival data and investigated with historical and newly obtained photometric and spectroscopic observations. The ZTF r and g data show a one magnitude deep, eclipse-like event with a duration of about half a year that occurred in 2022. The variability pattern of the star is further characterised by several dimming events in the optical region that are accompanied by simultaneous brightenings in the red and IR regions. Apart from that, two fast eruption-like events were recorded in ZTF r data. Archival data from WISE indicate long-term variability with a possible period of 6 or 12 yr. Our follow-up time series photometry reveals a stochastic short-term variability with an amplitude of about 0.1 mag on a timescale of about one hour. The spectral energy distribution is dominated by IR radiation. Our high-resolution spectroscopy shows strong forbidden emission lines from highly ionised species and symmetric double-peaked emission in Halpha, which is very different from what is seen in earlier spectra obtained in 2007. Several explanatory scenarios are presented. Our most likely interpretation is that our target object involves a hot central star surrounded by gaseous and dusty disks, an extended nebula, and a possible companion star.

Authors:M. Prišegen, N. Faltová

Abstract: Context: Open clusters (OCs) provide homogeneous samples of white dwarfs (WDs) with known distances, extinctions, and total ages. The unprecedented astrometric precision of \textit{\textit{Gaia}} allows us to identify many novel OC--WD pairs. Studying WDs in the context of their parent OCs makes it possible to determine the properties of WD progenitors and study the initial-final mass relation (IFMR). Aims: We seek to find potential new WD members of OCs in the solar vicinity. The analysis of OC members' parallaxes allows us to determine the OC distances to a high precision, which in turn enables us to calculate WD masses and cooling ages and to constrain the IFMR. Methods: We searched for new potential WD members of nearby OCs using the density-based machine learning clustering algorithm \texttt{HDBSCAN}. The clustering analysis was applied in five astrometric dimensions -- positions in the sky, proper motions and parallaxes -- and in three dimensions where the positional information was not considered in the clustering analysis. The identified candidate OC WDs were further filtered using the photometric criteria and properties of their putative host OCs. The masses and cooling ages of the WDs were calculated via a photometric method using all available \textit{\textit{Gaia}}, Pan-STARRS, SDSS, and GALEX photometry. The WD progenitor masses were determined using the ages and metallicities of their host OCs. Results: Altogether, 63 OC WD candidates were recovered, 27 of which are already known in the literature. We provide characterization for 36 novel WDs that have significant OC membership probabilities. Six of them fall into relatively unconstrained sections of the IFMR where the relation seems to exhibit nonlinear behavior. We were not able to identify any WDs originating from massive progenitors that would even remotely approach the widely adopted WD progenitor mass limit. (abridged)

Authors:Hongqiang Song, Leping Li, Zhenjun Zhou, Lidong Xia, Xin Cheng, Yao Chen

Abstract: Previous survey studies reported that coronal mass ejections (CMEs) can exhibit various structures in white-light coronagraphs, and $\sim$30\% of them have the typical three-part feature in the high corona (e.g., 2--6 $R_\odot$), which has been taken as the prototypical structure of CMEs. It is widely accepted that CMEs result from eruption of magnetic flux ropes (MFRs), and the three-part structure can be understood easily by means of the MFR eruption. It is interesting and significant to answer why only $\sim$30\% of CMEs have the three-part feature in previous studies. Here we conduct a synthesis of the CME structure in the field of view (FOV) of K-Coronagraph (1.05--3 $R_\odot$). In total, 369 CMEs are observed from 2013 September to 2022 November. After inspecting the CMEs one by one through joint observations of the AIA, K-Coronagraph and LASCO/C2, we find 71 events according to the criteria: 1) limb event; 2) normal CME, i.e., angular width $\geq$ 30$^{\circ}$; 3) K-Coronagraph caught the early eruption stage. All (or more than 90\% considering several ambiguous events) of the 71 CMEs exhibit the three-part feature in the FOV of K-Coronagraph, while only 30--40\% have the feature in the C2 FOV (2--6 $R_\odot$). For the first time, our studies show that 90--100\% and 30--40\% of normal CMEs possess the three-part structure in the low and high corona, respectively, which demonstrates that many CMEs can lose the three-part feature during their early evolutions, and strongly supports that most (if not all) CMEs have the MFR structures.

Authors:Muhammad Zain Mobeen, Tomasz Kamiński, Alexis Matter, Markus Wittkowski, John D. Monnier, Stefan Kraus, Jean-Baptiste Le Bouquin, Narsireddy Anugu, Theo Ten Brummelaar, Claire L. Davies, Jacob Ennis, Tyler Gardner, Aaron Labdon, Cyprien Lanthermann, Gail H. Schaefer, Benjamin R. Setterholm, Nour Ibrahim, Steve B. Howell

Abstract: V838 Mon is a stellar merger remnant that erupted in 2002 in a luminous red novae event. Although it is well studied in the optical, near infrared and submillimeter regimes, its structure in the mid-infrared wavelengths remains elusive. We observed V838 Mon with the MATISSE (LMN bands) and GRAVITY (K band) instruments at the VLTI and also the MIRCX/MYSTIC (HK bands) instruments at the CHARA array. We geometrically modelled the squared visibilities and the closure phases in each of the bands to obtain constraints on physical parameters. Furthermore, we constructed high resolution images of V838 Mon in the HK bands, using the MIRA and SQUEEZE algorithms to study the immediate surroundings of the star. Lastly, we also modelled the spectral features seen in the K and M bands at various temperatures. The image reconstructions show a bipolar structure that surrounds the central star in the post merger remnant. In the K band, the super resolved images show an extended structure (uniform disk diameter $\sim 1.94$ mas) with a clumpy morphology that is aligned along a north-west position angle (PA) of $-40^\circ$. Whereas in the H band, the extended structure (uniform disk diameter $\sim 1.18$ mas) lies roughly along the same PA. However, the northern lobe is slightly misaligned with respect to the southern lobe, which results in the closure phase deviations. The VLTI and CHARA imaging results show that V838 Mon is surrounded by features that resemble jets that are intrinsically asymmetric. This is also confirmed by the closure phase modelling. Further observations with VLTI can help to determine whether this structure shows any variation over time, and also if such bipolar structures are commonly formed in other stellar merger remnants.

Authors:H. Ernandes, M. J. Castro, B. Barbuy, M. Spite, V. Hill, B. Castilho, C. J. Evans

Abstract: We revisit the abundances of neutron-capture elements in the metal-poor ([Fe/H]=-2.9) r-process-rich halo star CS 31082-001. Partly motivated by the development of the new near-ultraviolet Cassegrain U-band Efficient Spectrograph for the Very Large Telescope, we compiled an expanded line list for heavy elements over the range 3000-4000 {\AA}, including hyperfine structure for several elements. Combining archival near-ultraviolet spectra of CS 31082-001 from the Hubble Space Telescope and the Very Large Telescope, we investigate the abundances and nucleosynthesis of 35 heavy elements (Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Os, Ir, Pt, Pb, Bi, Th, and U). Our analysis includes the first abundance estimates for tin, holmium, and ytterbium from these data, and the first for lutetium from ground-based data, enabling a more complete view of the abundance pattern of this important reference star. In general, the r-process dominated elements are as enhanced as those in the Sun, particularly for elements with Z $\ge$ 56 (Ba and heavier). However, the abundances for the lighter elements in our sample, from Ge to Sn (31 $\le$ Z $\le$ 50), do not scale with the solar abundance pattern. Moreover, the Ge abundance is deficient relative to solar, indicating that it is dominantly an iron-peak rather than neutron-capture element. Our results (or upper limits) on Sn, Pt, Au, Pb and Bi all pose further questions, prompting further study on the origin and evolution of the known r-rich and actinide-rich, metal-poor stars.

Authors:Michele Trabucchi

Abstract: Long-period variables are bright, evolved red giant stars showing periodic photometric changes due to stellar pulsation. They follow one or more period-luminosity and period-age relations, which make them highly promising distance indicators and tracers of young and intermediate-age stellar populations. Such a potential is especially interesting in view of the massive amount of data delivered by modern large-scale variability surveys. Crucially, these applications require a clear theoretical understanding of pulsation physics in connection with stellar evolution. Here, I describe an ongoing effort from our collaboration dedicated to the modelling of stellar pulsation in evolved stars, and how this work is impacting our capability of investigating long-period variables and exploiting them for other astrophysical studies. Furthermore, I present our ongoing work aimed at assessing the potential of semi-regular variables, an often neglected sub-type of long-period variables, to be distance indicators complementary to their better-known, more evolved counterparts, the Mira variables.

Authors:M. R. Drout, Y. Götberg, B. A. Ludwig, J. H. Groh, S. E. de Mink, A. J. G. O'Grady, N. Smith

Abstract: The theory of binary evolution predicts that many massive stars should lose their hydrogen-rich envelopes via interaction with a companion -- revealing hot helium stars with masses of $\sim$2--8M$_{\odot}$. However, only one candidate system had been identified, leaving a large discrepancy between theory and observation. Here, we present a new sample of stars -- identified via excess ultraviolet emission -- whose luminosities, colors, and spectral morphologies are consistent with predictions for the missing population. We detect radial velocity variations indicative of binary motion and measure high temperatures ($T_{\rm eff}\sim60-100$kK), high surface gravities ($\log(g)\sim5$) and depleted surface hydrogen mass fractions ($X_{\rm{H,surf}}\lesssim0.3$), which match expectations for stars with initial masses between 8--25 M$_{\odot}$ that have been stripped via binary interaction. These systems fill the helium star mass gap between subdwarfs and Wolf-Rayet stars, and are thought to be of large astrophysical significance as ionizing sources, progenitors of stripped-envelope supernovae and merging double neutron stars.

Authors:Y. Gotberg, M. R. Drout, A. P. Ji, J. H. Groh, B. A. Ludwig, P. A. Crowther, N. Smith, A. de Koter, S. E. de Mink

Abstract: Massive stars (~8-25Msun) stripped of their hydrogen-rich envelopes via binary interaction are thought to be the main progenitors for merging neutron stars and stripped-envelope supernovae. We recently presented the discovery of the first set of such stripped stars in a companion paper. Here, we fit the spectra of ten stars with new atmosphere models in order to constrain their stellar properties precisely. We find that the stellar properties align well with the theoretical expectations from binary evolution models for helium-core burning envelope-stripped stars. The fits confirm that the stars have high effective temperatures (Teff~50-100kK), high surface gravities (log g ~5), and hydrogen-poor/helium-rich surfaces (X(H, surf)~0-0.4) while showing for the first time a range of bolometric luminosities (10^3-10^5 Lsun), small radii (~0.5-1Rsun), and low Eddington factors (Gamma_e~0.006-0.4). Using these properties, we derive intermediate current masses (~1-8Msun), which suggest that their progenitors were massive stars (~5-25Msun) and that a subset will reach core-collapse, leaving behind neutron stars or black holes. Using the model fits, we also estimate the emission rates of ionizing photons for these stars, which agree well with previous model expectations. Further, by computing models for a range of mass-loss rates, we find that the stellar winds are weaker than predicted by any existing scheme (Mdot(wind)<~ 1e-9 Msun/yr). The properties of this first sample of intermediate mass helium stars suggest they both contain progenitors of type Ib and IIb supernovae, and provide important benchmarks for binary evolution and population synthesis models.

Authors:Axel Lazzarotto, Alain Hui-Bon-Hoa, Michel Rieutord

Abstract: Intermediate-mass stars are often fast rotators, and hence are centrifugally flattened and affected by gravity darkening. To analyse this kind of stars properly, one must turn to 2D models to compute the visible radiative flux and to take the geometrical effect of the star inclination into account. Assuming a given stellar age and chemical composition, we aim to derive the mass and rotation rates of main sequence fast rotating stars, along with their inclination, from photometric quantities. We chose three observables that vary with mass, rotation, and inclination: the infrared flux method temperature T_IRFM, the Str\"omgren c1 index, and a second index c2 built in the same way, but sensitive to the UV side of the Balmer jump. These observables are computed from synthetic spectra produced with the PHOENIX code and rely on a 2D stellar structure from the ESTER code. These quantities are computed for a grid of models in the range 2 to 7~M_Sun, and rotation rates from 30% to 80% of the critical rate. Then, for any triplet (T_IRFM, c1, c2), we try to retrieve the mass, rotation rate, and inclination using a Levenberg-Marquardt scheme, after a selection step to find the most suitable starting models. Hare-and-hound tests showed that our algorithm can recover the mass, rotation rate, and inclination with a good accuracy. The difference between input and retrieved parameters is negligible for models lying on the grid and is less than a few percent otherwise. An application to the real case of Vega showed that the u filter is located in a spectral region where the modelled and observed spectra are discrepant, and led us to define a new filter. Using this new filter and subsequent index, the Vega parameters are also retrieved with satisfactory accuracy. This work opens the possibility to determine the fundamental parameters of rapidly rotating early-type stars from photometric space observations.

Authors:S. S. Elgueta, N. Matsunaga, M. Jian, D. Taniguchi, N. Kobayashi, K. Fukue, S. Hamano, H. Sameshima, S. Kondo, A. Arai, Y. Ikeda, H. Kawakita, S. Otsubo, Y. Sarugaku, C. Yasui, T. Tsujimoto

Abstract: Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of loggf based on abundances of classical Cepheids obtained with optical spectra in Luck (2018), in order to establish the consistency between optical and infrared abundance results. Using time-series spectra of classical Cepheids obtained with WINERED spectrograph (0.97-1.35 $\mu$ m, R ~28000, we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (Teff), surface gravity (logg), microturbulence, and metallicity. With the newly calibrated relations of line-depth ratios (LDRs), we can achieve accuracy and precision comparable to optical studies (Luck 2018), with uncertainties of 90K and 0.108 dex for Teff, and log g, respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids (including neutron-capture elements), with loggf values that have been astrophysically calibrated.

Authors:Yoichi Takeda

Abstract: Gamma~Leo is a long-period visual binary system consisting of K0III (A) and G7III (B) giants, in which particular interest is attracted by the brighter A since the discovery of a planet around it. While detailed spectroscopic comparative study of both components would be worthwhile (e.g., for probing any impact of planet formation on chemical abundances), such a research seems to have been barely attempted as most available studies tend to be biased toward A. Given this situation, the physical properties of A and B along with their differences were investigated based on high-dispersion spectra in order to establish their stellar parameters, evolutionary status, and surface chemical compositions. The following results were obtained. (1) The masses were derived as ~1.7Msun and ~1.6Msun for A and B, respectively, both of which are likely to be in the stage of red clump giants after He-ignition. The mass of the planet around A has also been revised as m*sin(i) = 10.7M_Jupiter (increased by ~20%). (2) These are normal giants of subsolar metallicity ([Fe/H]~-0.4) belonging to the thin-disk population. (3) A as well as B show moderate C deficiency and N enrichment, which are in compatible with the prediction from the standard stellar evolution theory. (4) The chemical abundances of 26 elements are practically the same within <~0.1dex for both components, which implies that the surface chemistry is not appreciably affected by the existence of a planet in A.

Authors:Zhenyong Hou, Hui Tian, Wei Su, Maria S. Madjarska, Hechao Chen, Ruisheng Zheng, Xianyong Bai, Yuanyong Deng

Abstract: Type II radio bursts are often associated with coronal shocks that are typically driven by coronal mass ejections (CMEs) from the Sun. Here, we conduct a case study of a type II radio burst that is associated with a C4.5 class flare and a blowout jet, but without the presence of a CME. The blowout jet is observed near the solar disk center in the extreme-ultraviolet (EUV) passbands with different characteristic temperatures. Its evolution involves an initial phase and an ejection phase with a velocity of 560 km/s. Ahead of the jet front, an EUV wave propagates at a projected velocity of 403 km/s in the initial stage. The moving velocity of the source region of the type II radio burst is estimated to be 641 km/s, which corresponds to the shock velocity against the coronal density gradient. The EUV wave and the type II radio burst are closely related to the ejection of the blowout jet, suggesting that both are likely the manifestation of a coronal shock driven by the ejection of the blowout jet. The type II radio burst likely starts lower than those associated with CMEs. The combination of the velocities of the radio burst and the EUV wave yields a modified shock velocity at 757 km/s. The Alfven Mach number is in the range of 1.09-1.18, implying that the shock velocity is 10%-20% larger than the local Alfven velocity.

Authors:Andreea I. Henriksen National Space Institute, Technical University of Denmark, Elektrovej, Kgs. Lyngby, Denmark, Victoria Antoci National Space Institute, Technical University of Denmark, Elektrovej, Kgs. Lyngby, Denmark, Hideyuki Saio Astronomical Institute, Graduate School of Science, Tohoku University, Sendai, Japan, Frank Grundahl Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Aarhus C, Denmark, Hans Kjeldsen Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Aarhus C, Denmark, Timothy Van Reeth Institute of Astronomy, KU Leuven, Leuven, Belgium, Dominic M. Bowman Institute of Astronomy, KU Leuven, Leuven, Belgium, Péter I. Pápics Institute of Astronomy, KU Leuven, Leuven, Belgium, Peter De Cat Royal Observatory of Belgium, Brussels, Belgium, Joachim Krüger Centre for Astrophysics, University of Southern Queensland, Toowoomba, Australia Astronomical Observatory Institute, Faculty of Physics, A.Mickiewicz University, Poznan, Poland, M. Fredslund Andersen Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Aarhus C, Denmark, P. L. Pallé Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain Departamento de Astrofísica, Universidad de La Laguna

Abstract: Here we report an ensemble study of 214 A- and F-type stars observed by \textit{Kepler}, exhibiting the so-called \textit{hump and spike} periodic signal, explained by Rossby modes (r~modes) -- the \textit{hump} -- and magnetic stellar spots or overstable convective (OsC) modes -- the \textit{spike} -- respectively. We determine the power confined in the non-resolved hump features and find additional gravity~modes (g~modes) humps always occurring at higher frequencies than the spike. Furthermore, we derive projected rotational velocities from FIES, SONG and HERMES spectra for 28 stars and the stellar inclination angle for 89 stars. We find a strong correlation between the spike amplitude and the power in the r and g~modes, which suggests that both types of oscillations are mechanically excited by either stellar spots or OsC modes. Our analysis suggests that stars with a higher power in $m=1$ r~modes humps are more likely to also exhibit humps at higher azimuthal orders ($m$ = 2, 3, or 4). Interestingly, all stars that show g~modes humps are hotter and more luminous than the observed red edge of the $\delta$ Scuti instability strip, suggesting that either magnetic fields or convection in the outer layers could play an important role.

Authors:Xabier Perez-Couto, Jose Docobo, Pedro Campo

Abstract: The recent Gaia Data Release 3 has unveiled a catalog of over eight hundred thousand binary systems, providing orbital solutions for half of them. Since most of them are unresolved astrometric binaries, several astrophysical parameters that can be only derived from their relative orbits together with spectroscopic additional data, such as the individual stellar masses, remain unknown, and only the mass of the primary, m1, and a wide interval, [m2_lower, m2_upper], for the secondary companion of main-sequence binaries have been derived. To obtain the correct values for both components, in this paper, we describe an independent analytic algorithm to estimate the two most probable relative orbits and magnitude differences of a certain main-sequence or subgiant astrometric binary using all available Gaia data. Subsequently, both possible solutions are constrained to the one that is consistent with m1, m2_lower and m2_upper. Moreover, we deduce not only the correct values of the individual masses of each binary but also the size of the telescope necessary to resolve their components. The workflow of our algorithm as well as the ESMORGA (Ephemeris, Stellar Masses, and relative ORbits from GAia) catalog with more than one hundred thousand individual masses, spectral types, and effective temperatures derivated from its application are also presented.

Authors:Jeong-Eun Lee, Giseon Baek, Seokho Lee, Jae-Hong Jeong, Chul-Hwan Kim, Yuri Aikawa, Gregory J. Herczeg, Doug Johnstone, John J. Tobin

Abstract: We present the spectra of Complex Organic Molecules (COMs) detected in HOPS 373SW with the Atacama Large Millimeter/submillimeter Array (ALMA). HOPS 373SW, which is a component of a protostellar binary with a separation of 1500 au, has been discovered as a variable protostar by the JCMT Transient monitoring survey with a modest ~30% brightness increase at submillimeter wavelengths. Our ALMA Target of Opportunity (ToO) observation at ~345 GHz for HOPS 373SW revealed extremely young chemical characteristics with strong deuteration of methanol. The dust continuum opacity is very high toward the source center, obscuring line emission from within 0.03 arcsec. The other binary component, HOPS 373NE, was detected only in C17O in our observation, implying a cold and quiescent environment. We compare the COMs abundances relative to CH3OH in HOPS 373SW with those of V883 Ori, which is an eruptive disk object, as well as other hot corinos, to demonstrate the chemical evolution from envelope to disk. High abundances of singly, doubly, and triply deuterated methanol (CH2DOH, CHD2OH, and CD3OH) and a low CH3CN abundance in HOPS 373SW compared to other hot corinos suggest a very early evolutionary stage of HOPS 373SW in the hot corino phase. Since the COMs detected in HOPS 373SW would have been sublimated very recently from grain surfaces, HOPS 373SW is a promising place to study the surface chemistry of COMs in the cold prestellar phase, before sublimation.

Authors:Param Rekhi Weizmann Institute of Science, Israel, Sagi Ben-Ami Weizmann Institute of Science, Israel, Volker Perdelwitz Weizmann Institute of Science, Israel, Yossi Shvartzvald Weizmann Institute of Science, Israel

Abstract: M-dwarfs are common stellar hosts of habitable-zone exoplanets. NUV radiation can severely impact the atmospheric and surface conditions of such planets, making characterization of NUV flaring activity a key aspect in determining habitability. We use archival data from the GALEX and XMM-Newton telescopes to study the flaring activity of M-dwarfs in the NUV. The GALEX observations form the most extensive dataset of M-dwarfs in the NUV to date, with exploitation of this data possible due to the new gPhoton2 pipeline. We run a dedicated algorithm to detect flares in the pipeline produced lightcurves and find some of the most energetic flares observed to date within the NUV bandpass, with energies of $\sim 10^{34}$ ergs. Using GALEX data, we constrain flare frequency distributions for stars from M0 to M6 in the NUV up to $10^5$ s in equivalent duration and $10^{34}$ ergs in energy, orders of magnitude above any previous study in the UV. We estimate the combined effect of NUV luminosities and flare rates of stars later than M2 to be sufficient for abiogenesis on habitable zone exoplanets orbiting them. As a counterpoint, we speculate the high frequencies of energetic UV flares and associated coronal mass ejections would inhibit the formation of an ozone layer, possibly preventing genesis of complex Earth-like lifeforms due to sterilizing levels of surface UV radiation. We also provide a framework for future observations of M-dwarfs with ULTRASAT, a wide FoV NUV telescope to be launched in 2026.

Authors:Dominik R. G. Schleicher, Juan Pablo Hidalgo, Daniele Galli

Abstract: Chemically peculiar Ap and Bp stars host strong large-scale magnetic fields in the range of $200$~G up to $30$~kG, which are often considered to be the origin of fossil magnetic fields. We assess the evolution of such fossil fields during the star formation process and the pre-main sequence evolution of intermediate stars, considering fully convective models, models including a transition to a radiative protostar and models with a radiative core. We also examine the implications of the interaction between the fossil field and the core dynamo. We employ analytic and semi-analytic calculations combined with current observational constraints. For fully convective models, we show that magnetic field decay via convection can be expected to be very efficient for realistic parameters of turbulent resistivities. Based on the observed magnetic field strength - density relation, as well as the expected amount of flux loss due to ambipolar diffusion, it appears unlikely that convection could be suppressed via strong enough magnetic fields. On the other hand, a transition from a convective to a radiative core could very naturally explain the survival of a significant amount of flux, along with the presence of a critical mass. We show that in some cases, the interaction of a fossil field with a core dynamo may further lead to changes in the surface magnetic field structure. In the future, it will be important to understand in more detail how the accretion rate evolves as a function of time during the formation of intermediate-mass protostars, including its impact on the protostellar structure. The latter may even allow to derive quantitative predictions concerning the expected population of large scale magnetic fields in radiative stars.

Authors:B. T. Wang, X. Cheng, C. Li, J. Chen, M. D. Ding

Abstract: Remote brightenings often appear at outskirts of source active regions of solar eruptive events, nevertheless, their origin remains to be ascertained. In this study, we report imaging and spectroscopic observations of sequential remote brightenings with a combination of H$\alpha$ Imaging Spectrograph (HIS) onboard the Chinese H$\alpha$ Solar Explorer (CHASE), which is the first space-based solar telescope of China, and the Solar Dynamics Observatory. It is found that, during two successive M-class flares occurring on 2022 August 17, multiple ribbon-like brightenings appeared in sequence away from the flaring active region. Meanwhile, abundant cool filament materials moved downward to the sequential remote brightenings as visible at the H$\alpha$ red wing with a line-of-sight speed up to 70 km s$^{-1}$. The extrapolated three-dimensional magnetic field configuration shows that the sequential remote brightenings correspond to the footpoints of closed ambient field lines whose conjugate footpoints are rooted in the main flare site. We suggest that the sequential remote brightenings are most likely caused by the heating of interchange reconnection between the erupting flux rope and closed ambient field, during which the rope-hosting filament materials are transferred to the periphery of flaring active region along the closed ambient field rather than to the interplanetary space like in the scenario of the slow solar wind formation.

Authors:A. Moranchel-Basurto, D. Korčáková, R. O. Chametla

Abstract: We investigate the dynamic evolution of gaseous region around FS~CMa post-mergers. Due to the slow rotation of a central B-type star, the dynamics is driven mainly by the magnetic field of the central star. Recent observations have allowed us to set a realistic initial conditions such as, the magnetic field value ($B_\star\approx6\times10^{3}G$), the mass of the central star ($M_\star=6M_\odot$), and the initial disc density $\rho_{d0}\in[10^{-13}\mathrm{g\,cm^{-3}},10^{-11}\mathrm{g \, cm^{-3}}] $. We use the PLUTO code to perform 2.5D-MHD simulations of thin and thick discs models. Especially relevant for the interpretation of the observed properties of FS~CMa post-mergers are the results for low-density discs, in which we find formation of a jet emerging from inner edge of the disc, as well as the formation of the so called "hot plasmoid" in the corona region. Jets are probably detected as discrete absorption components in the resonance lines of FS~CMa stars. Moreover, the magnetic field configuration in the low-density plasma region, favors the appearance of magnetocentrifugal winds from the disc. The currents toward the star created by the magnetic field may explain accidentally observed material infall. The disc structure is significantly changed due to the presence of the magnetic field. The magnetic field is also responsible for the formation of a hot corona as observed in several FS~CMa stars through the Raman lines. Our results are valid for all magnetic stars surrounded by a low density plasma, i.e., some of stars showing the B[e] phenomenon.

Authors:Robert W. Dymott, Adrian J. Barker, Chris A. Jones, Steven M. Tobias

Abstract: We investigate the linear and nonlinear properties of the Goldreich-Schubert-Fricke (GSF) instability in stellar radiative zones with arbitrary local (radial and latitudinal) differential rotation. This instability may lead to turbulence that contributes to redistribution of angular momentum and chemical composition in stars. In our local Boussinesq model, we investigate varying the orientation of the shear with respect to the 'effective gravity', which we describe using the angle $\phi$. We first perform an axisymmetric linear analysis to explore the effects of varying $\phi$ on the local stability of arbitrary differential rotations. We then explore the nonlinear hydrodynamical evolution in three dimensions using a modified shearing box. The model exhibits both the diffusive GSF instability, and a non-diffusive instability that occurs when the Solberg-H\{o}iland criteria are violated. We observe the nonlinear development of strong zonal jets ("layering" in the angular momentum) with a preferred orientation in both cases, which can considerably enhance turbulent transport. By varying $\phi$ we find the instability with mixed radial and latitudinal shears transports angular momentum more efficiently (particularly if adiabatically unstable) than cases with purely radial shear $(\phi = 0)$. By exploring the dependence on box size, we find the transport properties of the GSF instability to be largely insensitive to this, implying we can meaningfully extrapolate our results to stars. However, there is no preferred length-scale for adiabatic instability, which therefore exhibits strong box-size dependence. These instabilities may contribute to the missing angular momentum transport required in red giant and subgiant stars and drive turbulence in the solar tachocline.

Authors:Harry J. Greatorex, Ryan O. Milligan, Phillip C. Chamberlin

Abstract: The chromospheric Lyman-alpha line of neutral hydrogen (Ly$\alpha$; 1216 \r{A}) is the most intense emission line in the solar spectrum, yet until recently observations of flare-related Ly$\alpha$ emission have been scarce. Here, we examine the relationship between nonthermal electrons accelerated during the impulsive phase of three M3 flares that were co-observed by RHESSI, GOES, and SDO, and the corresponding response of the chromosphere in Ly$\alpha$. Despite having identical X-ray magnitudes, these flares show significantly different Ly$\alpha$ responses. The peak Ly$\alpha$ enhancements above quiescent background for these flares were 1.5%, 3.3%, and 6.4%. However, the predicted Ly$\alpha$ enhancements from FISM2 were consistently <2.5%. By comparing the properties of the nonthermal electrons derived from spectral analysis of hard X-ray observations, flares with a harder spectral index were found to produce a greater Ly$\alpha$ enhancement. The percentage of nonthermal energy radiated by the Ly$\alpha$ line during the impulsive phase was found to range from 2.0-7.9%. Comparatively, the radiative losses in He II (304 \r{A}) were found to range from 0.6-1.4% of the nonthermal energy while displaying enhancements above the background of 7.3-10.8%. FISM2 was also found to underestimate the level of He II emission in two out of the three flares. These results may have implications for space weather studies and modelling the response of the terrestrial atmosphere to changes in the solar irradiance, and will guide the interpretation of flare-related Ly$\alpha$ observations that will become available during Solar Cycle 25.

Authors:Chase C. Million, Michael St. Clair, Scott W. Fleming, Luciana Bianchi, Rachel Osten

Abstract: We have performed the first systematic search of the full GALEX data archive for astrophysical variability on timescales of seconds to minutes by rebinning data across the whole mission to 30-second time resolution. The result is the GALEX Flare Catalog (GFCAT) which describes 1426 ultraviolet variable sources, including stellar flares, eclipsing binaries, $\delta$ Scuti and RR Lyrae variables, and Active Galactic Nuclei (AGN). Many of these sources have never previously been identified as variable. We have also assembled a table of observations of ultraviolet flares and accompanying statistics and measurements, including energies, and of candidate eclipsing stars. This effort was enabled by a significantly-enhanced version of the gPhoton software for analyzing time-domain GALEX data; this gPhoton2 package is available to support follow-on efforts.

Authors:Surajit Mondal, Divya Oberoi, Ayan Biswas, Devojyoti Kansabanik

Abstract: Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs) are a newly discovered class of radio emission from the solar corona. These emissions are characterized by their extremely impulsive, narrowband and ubiquitous nature. We have systematically been working on their detailed characterization, including their strengths, morphologies, temporal characteristics, energies, etc. This work is the next step in this series and focuses on the spectral nature of WINQSEs. Given that their strength is only a few percent of the background solar emission, we have adopted an extremely conservative approach to reliably identify WINQSES. Only a handful of WINQSEs meet all of our stringent criteria. Their flux densities lie in the 20 $-$ 50 Jy range and they have compact morphologies. For the first time, we estimate their bandwidths and find them to be less than 700 kHz, consistent with expectations based on earlier observations. Interestingly, we also find similarities between the spectral nature of WINQSEs and the solar radio spikes. This is consistent with our hypothesis that the WINQSEs are the weaker cousins of the type-III radio bursts and are likely to be the low-frequency radio counterparts of the nanoflares, originally hypothesized as a possible explanation for coronal heating.

Authors:Vitaly Akimkin, Alexei V. Ivlev, Paola Caselli, Munan Gong, Kedron Silsbee

Abstract: Dust coagulation in protoplanetary disks is not straightforward and is subject to several slow-down mechanisms, such as bouncing, fragmentation and radial drift to the star. Furthermore, dust grains in UV-shielded disk regions are negatively charged due to collisions with the surrounding electrons and ions, which leads to their electrostatic repulsion. For typical disk conditions, the relative velocities between micron-size grains are small and their collisions are strongly affected by the repulsion. On the other hand, collisions between pebble-size grains can be too energetic, leading to grain fragmentation. The aim of the present paper is to study a combined effect of the electrostatic and fragmentation barriers on dust evolution. We numerically solve the Smoluchowski coagulation-fragmentation equation for grains whose charging occurs under conditions typical for the inner disk regions, where thermal ionization operates. We find that dust fragmentation efficiently resupplies the population of small grains under the electrostatic barrier. As a result, the equilibrium abundance of sub-micron grains is enhanced by several orders of magnitude compared to the case of neutral dust. For some conditions with fragmentation velocities $\sim 1$ m s$^{-1}$, macroscopic grains are completely destroyed.

Authors:Kovi Rose, Joshua Pritchard, Tara Murphy, Manisha Caleb, Dougal Dobie, Laura Driessen, Stefan W. Duchesne, David L. Kaplan, Emil Lenc, Ziteng Wang

Abstract: We present the detection of rotationally modulated, circularly polarized radio emission from the T8 brown dwarf WISE J062309.94-045624.6 between 0.9 and 2.0 GHz. We detected this high proper motion ultracool dwarf with the Australian SKA Pathfinder in $1.36$ GHz imaging data from the Rapid ASKAP Continuum Survey. We observed WISE J062309.94-045624.6 to have a time and frequency averaged Stokes I flux density of $4.17\pm0.41$ mJy beam$^{-1}$, with an absolute circular polarization fraction of $66.3\pm9.0\%$, and calculated a specific radio luminosity of $L_{\nu}\sim10^{14.8}$ erg s$^{-1}$ Hz$^{-1}$. In follow-up observations with the Australian Telescope Compact Array and MeerKAT we identified a multi-peaked pulse structure, used dynamic spectra to place a lower limit of $B>0.71$ kG on the dwarf's magnetic field, and measured a $P=1.912\pm0.005$ h periodicity which we concluded to be due to rotational modulation. The luminosity and period we measured are comparable to those of other ultracool dwarfs observed at radio wavelengths. This implies that future megahertz to gigahertz surveys, with increased cadence and improved sensitivity, are likely to detect similar or later-type dwarfs. Our detection of WISE J062309.94-045624.6 makes this dwarf the coolest and latest-type star observed to produce radio emission.

Authors:A. Asensio Ramos, M. C. M. Cheung, I. Chifu, R. Gafeira

Abstract: The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field.

Authors:Zhenxin Lei, Ruijie He, Peter Nemeth, Xuan Zou, Huaping Xiao, Yong Yang, Jingkun Zhao

Abstract: Masses for 664 single-lined hot subdwarf stars identified in LAMOST were calculated by comparing synthetic fluxes from spectral energy distribution (SED) with observed fluxes from virtual observatory service. Three groups of hot subdwarf stars were selected from the whole sample according to their parallax precision to study the mass distributions. We found, that He-poor sdB/sdOB stars present a wide mass distribution from 0.1 to 1.0 $\mathrm{M}_{\odot}$ with a sharp mass peak around at 0.46 $\rm{M}_{\odot}$, which is consistent with canonical binary model prediction. He-rich sdB/sdOB/sdO stars present a much flatter mass distribution than He-poor sdB/sdOB stars and with a mass peak around 0.42 $\mathrm{M}_{\odot}$. By comparing the observed mass distributions to the predictions of different formation scenarios, we concluded that the binary merger channel, including two helium white dwarfs (He-WDs) and He-WD + main sequence (MS) merger, cannot be the only main formation channel for He-rich hot subdwarfs, and other formation channels such as the surviving companions from type Ia supernovae (SNe Ia) could also make impacts on producing this special population, especially for He-rich hot subdwarfs with masses less than 0.44 $\mathrm{M}_{\odot}$. He-poor sdO stars also present a flatter mass distribution with an inconspicuous peak mass at 0.18 $\mathrm{M}_{\odot}$. The similar mass - $\Delta RV_\mathrm{max}$ distribution between He-poor sdB/sdOB and sdO stars supports the scenario that He-poor sdO stars could be the subsequent evolution stage of He-poor sdB/sdOB stars.

Authors:S. Bellotti, R. Fares, A. A. Vidotto, J. Morin, P. Petit, G. A. J. Hussain, V. Bourrier, J. F. Donati, C. Moutou, E. Hebrard

Abstract: The space environment in which planets are embedded depends mainly on the host star and impacts the evolution of the planetary atmosphere. The quiet M dwarf GJ 436 hosts a close-in hot Neptune which is known to feature a comet-like tail of hydrogen atoms escaped from its atmosphere due to energetic stellar irradiation. Understanding such star-planet interactions is essential to shed more light on planet formation and evolution theories, in particular the scarcity of Neptune-size planets below 3 d orbital period, also known as ``Neptune desert''. We aimed at characterising the stellar environment around GJ 436, which requires an accurate knowledge of the stellar magnetic field. The latter is studied efficiently with spectropolarimetry, since it is possible to recover the geometry of the large-scale magnetic field by applying tomographic inversion on time series of circularly polarised spectra. We used spectropolarimetric data collected in the optical domain with Narval in 2016 to compute the longitudinal magnetic field, examine its periodic content via Lomb-Scargle periodogram and Gaussian Process Regression analysis, and finally reconstruct the large-scale field configuration by means of Zeeman-Doppler Imaging. We found an average longitudinal field of -12 G and a stellar rotation period of 46.6 d using a Gaussian Process model and 40.1 d using Zeeman-Doppler Imaging, both consistent with the literature. The Lomb-Scargle analysis did not reveal any significant periodicity. The reconstructed large-scale magnetic field is predominantly poloidal, dipolar and axisymmetric, with a mean strength of 16 G. This is in agreement with magnetic topologies seen for other stars of similar spectral type and rotation rate.

Authors:Vikrant V. Jadhav Uni. Bonn, Annapurni Subramaniam IIA, Ram Sagar IIA

Abstract: NGC 6791 is one of the richest old open clusters in the Milky Way. Its position above the Galactic plane and the number density makes it an interesting middle ground between Galactic open and globular clusters. We aim to detect the UV bright population of NGC 6791 using \textit{AstroSat}/UVIT images in near-UV and far-UV filters and characterise the known post mass transfer systems such as blue straggler stars (BSSs). We identified 20 members with large UV flux (out of 91 cluster members among 1180 detections), suggestive of binarity, interactions or stellar activity using multi-wavelength spectral energy distribution analysis. We characterised 62 isolated cluster members, including five hot subdwarfs (sdA/sdB). Additionally, we detected ten sdA/sdB/extremely low mass white dwarf (ELM) type candidates hidden alongside other cluster members. Additionally, we report the discovery of four candidate blue lurkers, which are main sequence stars with mass accretion history. We report that this cluster has a variety of stellar (pre-)remnants, such as sdBs, sdAs, and ELM white dwarfs, that are by-products of binary evolution. The above are likely to be post mass transfer binaries found throughout the evolutionary phases from the main sequence to the post horizontal branch. Therefore, this dynamically old open cluster is unique, making it an ideal testbed for dynamical studies.

Authors:W. S. Oh, T. Nordlander, G. S. Da Costa, M. S. Bessell, A. D. Mackey

Abstract: We present results of a search for extremely metal-poor (EMP) stars in the Large Magellanic Cloud, which can provide crucial information about the properties of the first stars as well as on the formation conditions prevalent during the earliest stages of star formation in dwarf galaxies. Our search utilised SkyMapper photometry, together with parallax and proper motion cuts (from Gaia), colour-magnitude cuts (by selecting the red giant branch region) and finally a metallicity-sensitive cut. Low-resolution spectra of a sample of photometric candidates were taken using the ANU 2.3m telescope/WiFeS spectrograph, from which 7 stars with [Fe/H] $\leq$ -2.75 were identified, two of which have [Fe/H] $\leq$ -3. Radial velocities, derived from the CaII triplet lines, closely match the outer rotation curve of the LMC for the majority of the candidates in our sample. Therefore, our targets are robustly members of the LMC based on their 6D phase-space information (coordinates, spectrophotometric distance, proper motions and radial velocities), and they constitute the most metal-poor stars so far discovered in this galaxy.

Authors:R. Fedriani, A. Caratti o Garatti, R. Cesaroni, J. C. Tan, B. Stecklum, L. Moscadelli, M. Koutoulaki, G. Cosentino, M. Whittle

Abstract: Massive stars have an impact on their surroundings from early in their formation until the end of their lives. However, very little is known about their formation. Episodic accretion may play a crucial role, but observations of these events have only been reported towards a handful of massive protostars. We aim to investigate the outburst event from the high-mass star-forming region S255IR where recently the protostar NIRS3 underwent an accretion outburst. We follow the evolution of this source both in photometry and morphology of its surroundings. Methods: We perform near-infrared adaptive optics observations on the S255IR central region using the Large Binocular Telescope in the K$_{\rm s}$ broad-band and the H$_2$ and Br$\gamma$ narrow-band filters with an angular resolution of $\sim0\farcs06$, close to the diffraction limit. We discover a new near-infrared knot north-east from NIRS3 that we interpret as a jet knot that was ejected during the last accretion outburst and observed in the radio regime as part of a follow-up after the outburst. We measure a mean tangential velocity for this knot of $450\pm50\,\mathrm{km\,s^{-1}}$. We analyse the continuum-subtracted images from H$_2$ which traces jet shocked emission, and Br$\gamma$ which traces scattered light from a combination of accretion activity and UV radiation from the central massive protostar. We observe a significant decrease in flux at the location of NIRS3, with K=13.48\,mag being the absolute minimum in the historic series. Our observations strongly suggest a scenario where the episodic accretion is followed by an episodic ejection response in the near-infrared, as it was seen in the earlier radio follow-up. The 30 years of $\sim2\,\mu{\rm m}$ photometry suggests that NIRS3 might have undergone another outburst in the late 1980s, being the first massive protostar with such evidence observed in the near-infrared.

Authors:Barbara Perri, Brigitte Schmieder, Pascal Démoulin, Stefaan Poedts, Florian Regnault

Abstract: The propagation of Interplanetary Coronal Mass Ejections (ICMEs) in the heliosphere is influenced by many physical phenomena, related to the internal structure of the ICME and its interaction with the ambient solar wind and magnetic field. As the solar magnetic field is modulated by the 11-year dynamo cycle, our goal is to perform a theoretical exploratory study to assess the difference of propagation of an ICME in typical minimum and maximum activity backgrounds. We define a median representative CME at 0.1~au, using both observations and numerical simulations, and describe it using a spheromak model. We use the heliospheric propagator European Heliospheric FORecasting Information Asset (EUHFORIA) to inject the same ICME in two different background wind environments. We then study how the environment and the internal CME structure impact the propagation of the ICME towards Earth, by comparison with an unmagnetized CME. At minimum of activity, the structure of the heliosphere around the ecliptic causes the ICME to slow down, creating a delay with the polar parts of the ejecta. This delay is more important if the ICME is faster. At maximum of activity, a southern coronal hole causes a northward deflection. For these cases, we always find that the ICME at maximum of activity arrives first, while the ICME at minimum of activity is actually more geo-effective. The helicity sign of the ICME is also a crucial parameter but at minimum of activity only, since it affects the magnetic profile and the arrival time of up to 8 hours.

Authors:Nagaraj Vernekar, Annapurni Subramaniam, Vikrant V. Jadhav, Dominic M. Bowman

Abstract: Blue straggler stars (BSSs) are formed through mass transfer or mergers in binaries. The recent detections of white dwarf (WD) companions to BSSs in M67 suggested a mass transfer pathway of formation. In search of a close companion to five BSSs in M67 that are known to be spectroscopic binaries, we study the light curves from K2 and TESS data. We use PHOEBE to analyse the light curves and estimate the properties of the companions. We detect variability in WOCS 1007, and the light curve is dominated by ellipsoidal variation. Using the light curve and radial velocity measurements, we estimate its orbital period to be 4.212$\pm$0.041 d and $e$ = 0.206$\pm$002. The mass of the companion is estimated to be 0.22$\pm$0.05 M$_{\odot}$ with a radius of 0.078$\pm$0.027 R$_{\odot}$, confirming it to be a low mass WD with T$_{\rm eff}$ = 14300$\pm$1100 K. The estimated mass of the BSS, 1.95$\pm$0.26 M$_{\odot}$, is similar to that estimated from isochrones. The BSS in WOCS 1007 shows $\delta$ Scuti pulsations, although it is slightly deformed and likely to be formed through an efficient mass transfer. Though we detect a light curve for WOCS 4003 showing grazing eclipse with ellipsoidal variation, the estimated parameters are inconclusive. Apart from the 0.44 d period, we found smaller eclipses with a period of 1.1 d, suggesting a compact triple system. In the case of WOCS 4003, WOCS 5005, and WOCS 1025, no eclipses or pulsations are detected, confirming the absence of any short-period inner binary with high inclination in these BSSs.

Authors:M. Latour, S. Hämmerich, M. Dorsch, U. Heber, T. -O. Husser, S. Kamann, S. Dreizler, J. Brinchmann

Abstract: In this work, we characterize the properties of HB stars in the GCs $\omega$ Cen and NGC 6752. We use dedicated model atmospheres and synthetic spectra grids computed using a hybrid LTE/NLTE modeling approach to fit the MUSE spectra of HB stars hotter than 8000 K in both clusters. The spectral fits provide estimates of the effective temperature, surface gravity, and helium abundance of the stars. The model grids are further used to fit the HST magnitudes, meaning the spectral energy distributions (SED), of the stars. From the SED fits, we derive the average reddening, radius, luminosity, and mass of the stars in our sample. The atmospheric and stellar properties that we derive for the stars in our sample are in good agreement with the theoretical expectations. In particular, the stars cooler than $\sim$15 000 K follow neatly the theoretical predictions on the radius, log $g$, and luminosity for helium-normal models. In $\omega$ Cen, we show that the majority of these cooler HB stars cannot originate from a helium-enriched population with $Y>$0.35. The properties of the hotter stars (radii and luminosities) are still in reasonable agreement with theoretical expectations, but the individual measurements have a large scatter. We use three different diagnostics, namely the position of the G-jump and changes in metallicity and helium abundances to place the onset of diffusion in the stellar atmospheres at Teff between 11 and 11.5 kK. Our sample includes two stars known as photometric variables, we confirm one to be a bona fide extreme HB object but the other is a blue straggler star. Finally, unlike what has been reported in the literature, we do not find significant differences between the properties of the stars in both clusters. We showed that our analysis method combining MUSE spectra and HST photometry of HB stars in GC is a powerful tool to characterize their stellar properties.

Authors:Alessandro Bruno, Georgia A. de Nolfo, James M. Ryan, Ian G. Richardson, Silvia Dalla

Abstract: Large solar eruptions are often associated with long-duration gamma-ray emission extending well above 100 MeV. While this phenomenon is known to be caused by high-energy ions interacting with the solar atmosphere, the underlying dominant acceleration process remains under debate. Potential mechanisms include continuous acceleration of particles trapped within large coronal loops or acceleration at coronal mass ejection (CME)-driven shocks, with subsequent back-propagation towards the Sun. As a test of the latter scenario, previous studies have explored the relationship between the inferred particle population producing the high-energy gamma-rays, and the population of solar energetic particles (SEPs) measured in situ. However, given the significant limitations on available observations, these estimates unavoidably rely on a number of assumptions. In an effort to better constrain theories of the gamma-ray emission origin, we re-examine the calculation uncertainties and how they influence the comparison of these two proton populations. We show that, even accounting for conservative assumptions related to gamma-ray flare, SEP event and interplanetary scattering modeling, their statistical relationship is only poorly/moderately significant. However, though the level of correlation is of interest, it does not provide conclusive evidence for or against a causal connection. The main result of this investigation is that the fraction of the shock-accelerated protons required to account for the gamma-ray observations is >20-40% for six of the fourteen eruptions analyzed. Such high values argue against current CME-shock origin models, predicting a <2% back-precipitation, hence the computed numbers of high-energy SEPs appear to be greatly insufficient to sustain the measured gamma-ray emission.

Authors:Abhishek K. Srivastava, Balveer Singh

Abstract: We describe a 2.5D MHD simulation describing the evolution of cool jets triggered by initial vertical velocity perturbations in the solar chromosphere. We implement random velocity pulses of amplitude 20-50 km/s between 1 Mm and 1.5 Mm, along with various switch-off periods between 50 s and 300 s. The applied vertical velocity pulses create a series of magnetoacoustic shocks steepening above TR. These shocks interact with each other in the inner corona, leading to complex localized velocity fields. The upward propagation of such perturbations creates low-pressure regions behind them, which propel a variety of cool jets and plasma flows. We study the transverse oscillations of a representative cool jet J1 , which moves up to the height of 6.2 Mm above the TR from its origin point. During its evolution, the plasma flows make the spine of jet J1 radially inhomogeneous, which is visible in the density and Alfv\'en speed smoothly varying across the jet. The highly dense J1 supports the propagating transverse wave of period of approximately 195 s with a phase speed of about 125 km/s. In the distance-time map of density, it is manifested as a transverse kink wave. However, the careful investigation of the distance-time maps of the x- and z-components of velocity reveals that these transverse waves are actually the mixed Alfv\'enic modes. The transverse wave shows evidence of damping in the jet. We conclude that the cross-field structuring of the density and characteristic Alfv\'en speed within J1 causes the onset of the resonant conversion and leakage of the wave energy outward to dissipate these transverse oscillations via resonant absorption. The wave energy flux is estimated as approximately of 1.0 x 10^6 ergs cm^{-2} s^{-1}. This energy, if it dissipates through the resonant absorption into the corona where the jet is propagated, is sufficient energy for the localized coronal heating.

Authors:Llorenç Melis, Roberto Soler, Jaume Terradas

Abstract: The fine structure of solar prominences is made by thin threads that outline the magnetic field lines. Observations show that transverse waves of Alfv\'enic nature are ubiquitous in prominence threads. These waves are driven at the photosphere and propagate to prominences suspended in the corona. Heating due to Alfv\'en wave dissipation could be a relevant mechanism in the cool and partially ionized prominence plasma. We explore the construction of 1D equilibrium models of prominence thin threads that satisfy energy balance between radiative losses, thermal conduction, and Alfv\'en wave heating. We assume the presence of a broadband driver at the photosphere that launches Alfv\'en waves towards the prominence. An iterative method is implemented, in which the energy balance equation and the Alfv\'en wave equation are consecutively solved. From the energy balance equation and considering no wave heating initially, we compute the equilibrium profiles along the thread of the temperature, density, ionisation fraction. We use the Alfv\'en wave equation to compute the wave heating rate, which is then put back in the energy balance equation to obtain new equilibrium profiles. The process is repeated until convergence to a self-consistent thread model heated by Alfv\'en waves is achieved. We have obtained equilibrium models composed of a cold and dense thread, a extremely thin PCTR, and an extended coronal region. The length of the cold thread decreases with the temperature at the prominence core and increases with the Alfv\'en wave energy flux. Equilibrium models are not possible for sufficiently large wave energy fluxes when the wave heating rate inside the cold thread becomes larger than radiative losses. The maximum value of the wave energy flux that allows an equilibrium depends on the prominence core temperature. This constrains the existence of equilibria in realistic conditions.

Authors:M. Rainer, S. Desidera, F. Borsa, D. Barbato, K. Biazzo, A. Bonomo, R. Gratton, S. Messina, G. Scandariato, L. Affer, S. Benatti, I. Carleo, L. Cabona, E. Covino, A. F. Lanza, R. Ligi, J. Maldonado, L. Mancini, D. Nardiello, D. Sicilia, A. Sozzetti, A. Bignamini, R. Cosentino, C. Knapic, A. F. Martínez Fiorenzano, E. Molinari, M. Pedani, E. Poretti

Abstract: The leading spectrographs used for exoplanets' sceince offer online data reduction softwares (DRS) that yield as an ancillary result the full-width at half-maximum (FWHM) of the cross-correlation function (CCF) that is used to estimate the radial velocity of the host star. The FWHM also contains information on the stellar projected rotational velocity vsini We wanted to establish a simple relationship to derive the vsini directly from the FWHM computed by the HARPS-N DRS in the case of slow-rotating solar-like stars. This may also help to recover the stellar inclination i, which in turn affects the exoplanets' parameters. We selected stars with an inclination of the spin axis compatible with 90 deg by looking at exoplanetary transiting systems with known small sky-projected obliquity: for these stars, we can presume that vsini is equal to stellar equatorial velocity veq. We derived their rotational periods from photometric time-series and their radii from SED fitting. This allowed us to recover their veq, which we could compare to the FWHM values of the CCFs obtained both with G2 and K5 spectral type masks. We obtained an empirical relation for each mask, useful for slow rotators (FWHM < 20 km/s). We applied them to 273 exoplanet-host stars observed with HARPS-N, obtaining homogeneous vsini measurements. We compared our results with the literature ones to confirm the reliability of our work, and we found a good agreement with the values found with more sophisticated methods for stars with log g > 3.5. We also tried our relations on HARPS and SOPHIE data, and we conclude that they can be used also on FWHM derived by HARPS DRS with G2 and K5 mask, and they may be adapted to the SOPHIE data as long as the spectra are taken in the high-resolution mode. We were also able to recover or constrain i for 12 objects with no prior vsini estimation.

Authors:M. B. Nielsen, G. R. Davies, W. J. Chaplin, W. H Ball, J. M. J. Ong, E. Hatt, B. P. Jones, M. Logue

Abstract: The asteroseismic analysis of stellar power density spectra is often computationally expensive. The models used in the analysis may use several dozen parameters to accurately describe features in the spectra caused by oscillation modes and surface granulation. Many parameters are often highly correlated, making the parameter space difficult to quickly and accurately sample. They are, however, all dependent on a smaller set of parameters, namely the fundamental stellar properties. We aim to leverage this to simplify the process of sampling the model parameter space for the asteroseismic analysis of solar-like oscillators, with an emphasis on mode identification. Using a large set of previous observations, we applied principal component analysis to the sample covariance matrix to select a new basis on which to sample the model parameters. Selecting the subset of basis vectors that explains the majority of the sample variance, we redefine the model parameter prior probability density distributions in terms of a smaller set of latent parameters. We are able to reduce the dimensionality of the sampled parameter space by a factor of two to three. The number of latent parameters needed to accurately model the stellar oscillation spectra cannot be determined exactly but is likely only between four and six. Using two latent parameters, the method is able to describe the bulk features of the oscillation spectrum, while including more latent parameters allows for a frequency precision better than $\approx10\%$ of the small frequency separation for a given target. We find that sampling a lower-rank latent parameter space still allows for accurate mode identification and parameter estimation on solar-like oscillators over a wide range of evolutionary stages. This allows for the potential to increase the complexity of spectrum models without a corresponding increase in computational expense.

Authors:Paul Heeren Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Germany Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark, René Tronsgaard Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark, Frank Grundahl Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark, Sabine Reffert Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Germany, Andreas Quirrenbach Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Germany, Pere L. Pallé Instituto de Astrofísica de Canarias, Tenerife, Spain Universidad de La Laguna

Abstract: For existing and future projects dedicated to measuring precise radial velocities (RVs), we have created an open-source, flexible data reduction software to extract RVs from \'echelle spectra via the iodine (I$_2$) absorption cell method. The software, called $pyodine$, is completely written in Python and has been built in a modular structure to allow for easy adaptation to different instruments. We present the fundamental concepts employed by $pyodine$, which build on existing I$_2$ reduction codes, and give an overview of the software's structure. We adapted $pyodine$ to two instruments, Hertzsprung SONG located at Teide Observatory (SONG hereafter) and the Hamilton spectrograph at Lick Observatory (Lick hereafter), and demonstrate the code's flexibility and its performance on spectra from these facilities. Both for SONG and Lick data, the $pyodine$ results generally match the RV precision achieved by the dedicated instrument pipelines. Notably, our code reaches a precision of roughly $0.69 \,m\,s^{-1}$ on a short-term solar time series of SONG spectra, and confirms the planet-induced RV variations of the star HIP~36616 on spectra from SONG and Lick. Using the solar spectra, we also demonstrate the capabilities of our software in extracting velocity time series from single absorption lines. A probable instrumental effect of SONG is still visible in the $pyodine$ RVs, despite being a bit damped as compared to the original results. With $pyodine$ we prove the feasibility of a highly precise, yet instrument-flexible I$_2$ reduction software, and in the future the code will be part of the dedicated data reduction pipelines for the SONG network and the Waltz telescope project in Heidelberg.

Authors:E. Marini, C. Ventura, M. Tailo, P. Ventura, F. Dell'Agli, M. Castellani

Abstract: The binary star alpha Aurigae (otherwise known as Capella) is extremely important to understand the core hydrogen and helium burning phases of the stars, as the primary star is likely evolving through the core helium burning phase, and the masses of the two components are 2.5 Msun and 2.6 Msun, which fall into a mass range for which the extention of the core overshoot during the main sequence phase is uncertain. We aim at deriving the extent of the core overshoot experienced during the core burning phases and testing the efficiency of the convective transport of energy in the external envelope, by comparing results from stellar evolution modelling with the results from the observations. We consider evolutionary tracks calculated on purpose for the present work, for the primary and secondary star of Capella. We determine the extent of the extra-mixing from the core during the main sequence evolution and the age of the system, by requiring that the effective temperatures and surface gravities of the model stars reproduce those derived from the observations at the same epoch. We further check consistency between the observed and predicted surface chemistry of the stars. Consistency between results from stellar evolution modelling and the observations of Capella is found when extra-mixing from the core is assumed, the extent of the extra-mixed zone being of the order of 0.25 H_P. The age of the system is estimated to be 710 Myr. These results allow to nicely reproduce the observed surface chemistry, particularly the recent determination of the 12C/13C ratio based on LBT (Large Binocular Telescope) and VATT (Vatican Advanced Technology Telescope) observations

Authors:J. Merc, R. Gális, M. Wolf, P. A. Dubovský, J. Kára, F. Sims, J. R. Foster, T. Medulka, C. Boussin, J. P. Coffin, C. Buil, D. Boyd, J. Montier

Abstract: V503 Her was previously proposed as an eclipsing symbiotic candidate based on photometric behavior and spectroscopic appearance indicating the composite optical spectrum. To investigate its nature, we analyzed long-term photometric observations covering one hundred years of its photometric history and new low-resolution optical spectroscopic data, supplemented with the multifrequency measurements collected from several surveys and satellites. Based on the analysis presented in this paper, we claim that V503 Her is not an eclipsing binary star. The optical and infrared wavelengths are dominated by a K-type bright giant with an effective temperature of 4 500 K, luminosity of 1 900 L$_\odot$, and sub-solar metallicity on the asymptotic giant branch showing semiregular complex multi-periodic pulsation behavior. V503 Her does not show the characteristics of strongly interacting symbiotic variables, but some pieces of evidence suggest that it could still be one of the 'hidden' accreting-only symbiotic systems. However, the currently available data do not allow us to fully confirm or constrain the parameters of a possible companion.

Authors:J. Labadie-Bartz, S. Hümmerich, K. Bernhard, E. Paunzen, M. E. Shultz

Abstract: High-quality light curves from space missions have opened up a new window on the rotational and pulsational properties of magnetic chemically peculiar (mCP) stars and have fuelled asteroseismic studies. They allow the internal effects of surface magnetic fields to be probed and numerous astrophysical parameters to be derived with great precision. We present an investigation of the photometric variability of a sample of 1002 mCP stars discovered in the LAMOST archival spectra with the aims of measuring their rotational periods and identifying interesting objects for follow-up studies. TESS photometry was available for 782 mCP stars and was analysed using a Fourier two-term frequency fit to determine the stars' rotational periods. The rotational signal was then subtracted from the light curve to identify non-rotational variability. A pixel-level blending analysis was performed to check whether the variability originates in the target star or a nearby blended neighbour. We investigated correlations between the rotational periods, fractional age on the main sequence, mass, and several other observables. We present rotational periods and period estimates for 720 mCP stars. In addition, we identified four eclipsing binary systems that likely host an mCP star, as well as 25 stars with additional signals consistent with pulsation (12 stars with frequencies above 10 d$^{-1}$ and 13 stars with frequencies below 10 $^{-1}$). We find that more evolved stars have longer rotation periods, in agreement with the assumption of the conservation of angular momentum during main-sequence evolution. With our work, we increase the sample size of mCP stars with known rotation periods and identify prime candidates for detailed follow-up studies. This enables two paths towards future investigations: population studies of even larger samples of mCP stars and the detailed characterisation of high-value targets.

Authors:S. Das, L. Molnár, S. M. Kanbur, M. Joyce, A. Bhardwaj, H. P. Singh, M. Marconi, V. Ripepi, R. Smolec

Abstract: We present new theoretical period--luminosity (PL) and period--radius (PR) relations at multiple wavelengths (Johnson--Cousins--Glass and {\sl Gaia} passbands) for a fine grid of BL~Herculis models computed using {\sc mesa-rsp}. The non-linear models were computed for periods typical of BL~Her stars, i.e. $1\leq P ({\rm days}) \leq4$, covering a wide range of input parameters: metallicity ($-$2.0 dex $\leq$ [Fe/H] $\leq$ 0.0 dex), stellar mass (0.5--0.8 M$_{\odot}$), luminosity (50--300 L$_{\odot}$) and effective temperature (full extent of the instability strip; in steps of 50K). We investigate the impact of four sets of convection parameters on multi-wavelength properties. Most empirical relations match well with theoretical relations from the BL~Her models computed using the four sets of convection parameters. No significant metallicity effects are seen in the PR relations. Another important result from our grid of BL~Her models is that it supports combining PL relations of RR Lyrae and Type~II Cepheids together as an alternative to classical Cepheids for the extragalactic distance scale calibration.

Authors:Emily I. Mason, Roberto Lionello, Cooper Downs, Jon A. Linker, Ronald M. Caplan

Abstract: We present in this Letter the first global comparison between traditional line-tied steady state magnetohydrodynamic models and a new, fully time-dependent thermodynamic magnetohydrodynamic simulation of the global corona. The maps are scaled to the approximate field distributions and magnitudes around solar minimum using the Lockheed Evolving Surface-Flux Assimilation Model to incorporate flux emergence and surface flows over a full solar rotation, and include differential rotation and meridional flows. Each time step evolves the previous state of the plasma with a new magnetic field input boundary condition. We find that this method is a significant improvement over steady-state models, as it closely mimics the constant photospheric driving on the Sun. The magnetic energy levels are higher in the time-dependent model, and coronal holes evolve more along the following edge than they do in steady-state models. Coronal changes, as illustrated with forward-modeled emission maps, evolve on longer timescales with time-dependent driving. We discuss implications for active and quiet Sun scenarios, solar wind formation, and widely-used steady state assumptions like potential field source surface calculations.

Authors:Thallis Pessi, Jose L. Prieto, Joseph P. Anderson, Lluís Galbany, Joseph D. Lyman, Christopher Kochanek, Subo Dong, Francisco Forster, Raul González-Díaz, Santiago Gonzalez-Gaitan, Claudia P. Gutiérrez, Thomas W. -S. Holoien, Philip A. James, Cristina Jiménez-Palau, Evelyn J. Johnston, Hanindyo Kuncarayakti, Fabián Rosales-Ortega, Sebastian F. Sánchez, Steve Schulze, Benjamin Shappee

Abstract: The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the VLT enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the ASAS-SN survey has enabled us to perform a minimally biased statistical analysis of CCSN environments. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the the AMUSING survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all HII regions detected within each galaxy, including the star formation rate (SFR), H$\alpha$ equivalent width (EW), oxygen abundance, and extinction. We found that stripped-envelope (SE) SNe occur in environments with a higher median SFR, H$\alpha$ EW, and oxygen abundances than SNe II and SNe IIn/Ibn. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, H$\alpha$ EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and H$\alpha$ EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, $s$, of SNe II correlates with the H$\alpha$ EW, and that the luminosity and the $\Delta m_{15}$ parameter of SESNe correlate with the oxygen abundance, H$\alpha$ EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

Authors:Thallis Pessi, Joseph P. Anderson, Joseph D. Lyman, Jose L. Prieto, Lluís Galbany, Christopher S. Kochanek, Sebastian F. Sánchez, Hanindyo Kuncarayakti

Abstract: Core-collapse supernovae (CCSNe) are widely accepted to be caused by the explosive death of massive stars with initial masses $\gtrsim 8$M$_\odot$. There is, however, a comparatively poor understanding of how properties of the progenitors -- mass, metallicity, multiplicity, rotation etc. -- manifest in the resultant CCSN population. Here we present a minimally biased sample of nearby CCSNe from the ASAS-SN survey whose host galaxies were observed with integral-field spectroscopy using MUSE at the VLT. This dataset allows us to analyze the explosion sites of CCSNe within the context of global star formation properties across the host galaxies. We show that the CCSN explosion site oxygen abundance distribution is offset to lower values than the overall HII region abundance distribution within the host galaxies. We further show that within the subsample of low-metallicity host galaxies, the CCSNe unbiasedly trace the star-formation with respect to oxygen abundance, while for the sub-sample of higher-metallicity host galaxies, they preferentially occur in lower-abundance star-forming regions. We estimate the occurrence of CCSNe as a function of oxygen abundance per unit star formation, and show that there is a strong decrease as abundance increases. Such a strong and quantified metallicity dependence on CCSN production has not been shown before. Finally, we discuss possible explanations for our result and show that each of these has strong implications for our understanding of CCSNe and massive star evolution.

Authors:Jia Zhang, Sheng-Bang Qian, Guo-Bao Zhang, Xiao Zhou

Abstract: We collected a total of 4,058 X-ray binary stars, out of which 339 stars had three atmospheric parameters for optical companions from Gaia and LAMOST, while 264 stars had masses and radii of optical companions determined using stellar evolution models. We conducted a thorough discussion on the reliability of each parameter. The statistical analysis revealed a noticeable bimodal distribution in the mass, radius, and age of the optical components. Our findings led to the proposal of a new quantitative classification criterion for X-ray binary stars. In this classification, one type is categorized as high-mass, high-temperature, and young, while the other type is classified as low-mass, low-temperature, and old, corresponding to High-Mass X-Ray Binaries (HMXBs) and Low-Mass X-Ray Binaries (LMXBs), respectively. The dividing lines were established at 11,500 K, 1.7 $M_{\odot}$, and 0.14 Gyr. The classification results of the three parameters showed consistency with one another in 90\% of the cases and were in agreement with previous classifications in 80\% of the cases. We found that the parameters of the two types had well-defined boundaries and distinct patterns. Based on our findings, we suggest that temperature is the best parameter for classification. Therefore, we propose that X-ray binary stars should be classified into high-temperature X-ray binaries (HTXBs) and low-temperature X-ray binaries (LTXBs). We believe that this classification is more convenient in practice and aligns well with physics.

Authors:Sumanth A. Rotti, Petrus C. Martens

Abstract: Solar energetic particle (SEP) events are one of the most crucial aspects of space weather. Their prediction depends on various factors including the source solar eruptions such as flares and coronal mass ejections (CMEs). The Geostationary Solar Energetic Particle (GSEP) Events catalog was developed as an extensive data set towards this effort for solar cycles 22, 23 and 24. In the present work, we review and extend the GSEP data set by; (1) adding "weak" SEP events that have proton enhancements from 0.5 to 10 pfu in the E>10 MeV channel, and (2) improving the associated solar source eruptions information. We analyze and discuss spatio-temporal properties such as flare magnitudes, locations, rise times, and speed and width of CMEs. We check for the correlation of these parameters with peak proton fluxes and event fluences. Our study also focuses on understanding feature importance towards the optimal performance of machine learning (ML) models for SEP event forecasting. We implement random forest (RF), extreme gradient boosting (XGBoost), logistic regression (LR) and support vector machines (SVM) classifiers in a binary classification schema. Based on the evaluation of our best models, we find both the flare and CME parameters are requisites to predict the occurrence of an SEP event. This work is a foundation for our further efforts on SEP event forecasting using robust ML methods.

Authors:L. Roberti, M. Pignatari, A. Psaltis, A. Sieverding, P. Mohr, Zs. Fülöp, M. Lugaro

Abstract: The $\gamma$-process nucleosynthesis in core-collapse supernovae is generally accepted as a feasible process for the synthesis of neutron-deficient isotopes beyond iron. However, crucial discrepancies between theory and observations still exist: the average production of $\gamma$-process yields from massive stars are too low to reproduce the solar distribution in galactic chemical evolution calculations, and the yields of the Mo and Ru isotopes are by a further factor of 10 lower than the yields of the other $\gamma$-process nuclei. We investigate the $\gamma$-process in 5 sets of core-collapse supernova models published in literature with initial masses 15, 20, and 25 M$_{\odot}$ at solar metallicity. We compared the $\gamma$-process overproduction factors from the different models. To highlight the possible effect of nuclear physics input, we also considered 23 ratios of two isotopes close to each other in mass, relative to their solar values. Further, we investigated the contribution of C-O shell mergers in the supernova progenitors as an additional site of the $\gamma$-process. Our analysis shows that a large scatter among the different models exists for both the $\gamma$-process integrated yields and the isotopic ratios. We found only 10 ratios that agree with their solar values, all the others differ by at least a factor of 3 from the solar values in all the considered sets of models. The $\gamma$-process within C-O shell mergers mostly influence the isotopic ratios that involve intermediate and heavy proton-rich isotopes with $\rm A>100$.

Authors:Stéphane Mathis, Lisa Bugnet

Abstract: Space asteroseismology is revolutionizing our knowledge of the internal structure and dynamics of stars. A breakthrough is ongoing with the recent discoveries of signatures of strong magnetic fields in the core of red giant stars. The key signature for such a detection is the asymmetry these fields induce in the frequency splittings of observed dipolar mixed gravito-acoustic modes. We investigate the ability of the observed asymmetries of the frequency splittings of dipolar mixed modes to constrain the geometrical properties of deep magnetic fields. We use the powerful analytical Racah-Wigner algebra used in Quantum Mechanics to characterize the geometrical couplings of dipolar mixed oscillation modes with various possible realistic fossil magnetic fields' topologies and compute the induced perturbation of their frequencies. First, in the case of an oblique magnetic dipole, we provide the exact analytical expression of the asymmetry as a function of the angle between the rotation and magnetic axes. Its value provides a direct measure of this angle. Second, considering a combination of axisymmetric dipolar and quadrupolar fields, we show how the asymmetry is blind to unravel the relative strength and sign of each component. Finally, in the case of a given multipole, we show that a negative asymmetry is a signature of non-axisymmetric topologies. Therefore, asymmetries of dipolar mixed modes provide key but only partial information on the geometrical topology of deep fossil magnetic fields. Asteroseismic constraints should therefore be combined with spectropolarimetric observations and numerical simulations, which aim to predict the more probable stable large-scale geometries.

Authors:A. Papageorgiou, P. -E. Christopoulou, E. Lalounta, C. E. Ferreira Lopes, M. Catelan, A. J. Drake, P. Xantzios, I. Alikakos

Abstract: We present a multi-band photometric analysis of CRTS J163819.6+03485, the first low mass ratio (LMR) contact binary system with a period under the contact binary (CB) period limit. The unprecedented combination of mass ratio and period makes this system unique for eclipsing binary (EB) research. Using new multi-band photometric observations, we explored the parameter space of this unique total EB system through a detailed scan in the mass ratio - inclination plane and using the PIKAIA genetic algorithm optimizer. The best set of relative physical parameters and corresponding uncertainties was adopted through Markov Chain Monte Carlo sampling of the parameter space. The resulting mass ratio of the system is $q = 0.16 \pm 0.01$. The absolute parameters were derived by adopting an empirical mass-luminosity relation. Period changes are also investigated by using new observations and archival photometric light curves from massive astronomical surveys, which revealed in a preliminary solution the presence of a possible low-mass tertiary companion. The origin and evolutionary status of the system are investigated through the detached-binary formation scenario.

Authors:Savita Mathur, Zachary R. Claytor, Angela R. G. Santos, Rafael A. García, Louis Amard, Lisa Bugnet, Enrico Corsaro, Alfio Bonanno, Sylvain N. Breton, Diego Godoy-Rivera, Marc H. Pinsonneault, Jennifer van Saders

Abstract: The ages of solar-like stars have been at the center of many studies such as exoplanet characterization or Galactic-archaeology. While ages are usually computed from stellar evolution models, relations linking ages to other stellar properties, such as rotation and magnetic activity, have been investigated. With the large catalog of 55,232 rotation periods, $P_{\rm rot}$, and photometric magnetic activity index, $S_{\rm ph}$ from Kepler data, we have the opportunity to look for such magneto-gyro-chronology relations. Stellar ages are obtained with two stellar evolution codes that include treatment of angular momentum evolution, hence using $P_{\rm rot}$ as input in addition to classical atmospheric parameters. We explore two different ways of predicting stellar ages on three subsamples with spectroscopic observations: solar analogs, late-F and G dwarfs, and K dwarfs. We first perform a Bayesian analysis to derive relations between $S_{\rm ph}$ and ages between 1 and 5 Gyr, and other stellar properties. For late-F and G dwarfs, and K dwarfs, the multivariate regression favors the model with $P_{\rm rot}$ and $S_{\rm ph}$ with median differences of 0.1%.and 0.2% respectively. We also apply Machine Learning techniques with a Random Forest algorithm to predict ages up to 14 Gyr with the same set of input parameters. For late-F, G and K dwarfs together, predicted ages are on average within 5.3% of the model ages and improve to 3.1% when including $P_{\rm rot}$. These are very promising results for a quick age estimation for solar-like stars with photometric observations, especially with current and future space missions.

Authors:Landstreet, J. D., Villaver, E., Bagnulo, S

Abstract: WD0810-353 is a white dwarf within the 20pc volume around the Sun. Using Gaia astrometric distance and proper motions, and a radial velocity derived from Gaia spectroscopy, it has been predicted that this star will pass within 1pc of the Solar System in about 30kyr. However, WD0810-353 has been also shown to host a magnetic field with strength of the order of 30MG. Its spectrum is therefore not like those of normal DA stars of similar effective temperature. We have obtained and analysed new polarised spectra of the star around Halpha. Our analysis suggests that the visible surface of the star shows two regions of different field strength (~30 and ~45MG, respectively), and opposite polarity. The spectra do not change over a 4 year time span, meaning that either the stellar rotation period is no shorter than several decades, or that the field is symmetric about the rotation axis. Taking into account magnetic shift and splitting, we obtain an estimate of the radial velocity of the star (+83+/- 140km/s); we reject both the value an the claimed precision deduced from the Gaia DR3 spectroscopy (-373.7+/- 8.2km/s), and we conclude that there will probably be no close encounter between the Solar System and WD0810-353. We also reject the suggestion that the star is a hypervelocity runaway star, a survivor of a Type Ia Supernova explosion. It is just a stellar remnant in the Solar neighborhood with a very strong and complex magnetic field.

Authors:Ludovic Petitdemange, Florence Marcotte, Christophe Gissinger, Florentin Daniel

Abstract: The Tayler-Spruit dynamo mechanism has been proposed two decades ago as a plausible mechanism to transport angular momentum in radiative stellar layers. Direct numerical simulations are still needed to understand its trigger conditions and the saturation mechanisms. The present study follows up on (Petitdemange et al. 2023), where we reported the first numerical simulations of a Tayler-Spruit dynamo cycle. Here we extend the explored parameter space to assess in particular the influence of stratification on the dynamo solutions. We also present numerical verification of theoretical assumptions made in (Spruit 2002), which are instrumental in deriving the classical prescription for angular momentum transport implemented in stellar evolution codes. A simplified radiative layer is modeled numerically by considering the dynamics of a stably-stratified, differentially rotating, magnetized fluid in a spherical shell. Our simulations display a diversity of magnetic field topologies and amplitudes depending on the flow parameters, including hemispherical solutions. The Tayler-Spruit dynamos reported here are found to satisfy magnetostrophic equilibrium and achieve efficient turbulent transport of angular momentum, following Spruit's heuristic prediction.

Authors:Gautham N. Sabhahit, Jorick S. Vink, Andreas A. C. Sander, Erin R. Higgins

Abstract: Very massive stars (VMS) up to 200-300 $M_\odot$ have been found in the Local Universe. If they would lose little mass they produce intermediate-mass black holes or pair-instability supernovae (PISNe). Until now, VMS modellers have extrapolated mass-loss vs. metallicity ($Z$) exponents from optically-thin winds, resulting in a range of PISN thresholds that might be unrealistically high in $Z$, as VMS develop optically-thick winds. We utilize the transition mass-loss rate of Vink and Gr\"afener (2012) that accurately predicts mass-loss rates of Of/WNh ("slash") stars that characterize the morphological transition from absorption-dominated O-type spectra to emission-dominated WNh spectra. We develop a wind efficiency framework, where optically thin winds transition to enhanced winds, enabling us to study VMS evolution at high redshift where individual stars cannot be resolved. We present a MESA grid covering $Z_\odot/2$ to $Z_\odot/100$. VMS above the transition evolve towards lower luminosity, skipping the cool supergiant phase but directly forming pure He stars at the end of hydrogen burning. Below the transition, VMS evolve as cooler luminous blue variables (LBVs) or yellow hypergiants (YHGs), naturally approaching the Eddington limit. Strong winds in this YHG/LBV regime -- combined with a degeneracy in luminosity -- result in a mass-loss runaway where a decrease in mass increases wind mass loss. Our models indicate an order-of-magnitude lower threshold than usually assumed, at $Z_\odot/20$ due to our mass-loss runaway. While future work on LBV mass loss could affect the PISN threshold, our framework will be critical for establishing definitive answers on the PISN threshold and galactic chemical evolution modelling.

Authors:Siemen Burssens, Dominic M. Bowman, Mathias Michielsen, Sergio Simón-Díaz, Conny Aerts, Vincent Vanlaer, Gareth Banyard, Nicolas Nardetto, Richard H. D. Townsend, Gerald Handler, Joey S. G. Mombarg, Roland Vanderspek, George Ricker

Abstract: Massive stars are progenitors of supernovae, neutron stars and black holes. During the hydrogen-core burning phase their convective cores are the prime drivers of their evolution, but inferences of core masses are subject to unconstrained boundary mixing processes. Moreover, uncalibrated transport mechanisms can lead to strong envelope mixing and differential radial rotation. Ascertaining the efficiency of the transport mechanisms is challenging because of a lack of observational constraints. Here we deduce the convective core mass and robustly demonstrate non-rigid radial rotation in a supernova progenitor, the $12.0^{+1.5}_{-1.5}$ solar-mass hydrogen-burning star HD 192575, using asteroseismology, TESS photometry, high-resolution spectroscopy, and Gaia astrometry. We infer a convective core mass ($M_{\rm cc} = 2.9^{+0.5}_{-0.8}$ solar masses), and find the core to be rotating between 1.4 and 6.3 times faster than the stellar envelope depending on the location of the rotational shear layer. Our results deliver a robust inferred core mass of a massive star using asteroseismology from space-based photometry. HD 192575 is a unique anchor point for studying interior rotation and mixing processes, and thus also angular momentum transport mechanisms inside massive stars.

Authors:N. Walters, J. Farihi, P. Dufour, J. S. Pineda, R. G. Izzard

Abstract: White dwarfs stars are known to be polluted by their active planetary systems, but little attention has been paid to the accretion of wind from low-mass companions. The capture of stellar or substellar wind by white dwarfs is one of few methods available to astronomers which can assess mass-loss rates from unevolved stars and brown dwarfs, and the only known method to extract their chemical compositions. In this work, four white dwarfs with closely-orbiting, L-type brown dwarf companions are studied to place limits on the accretion of a substellar wind, with one case of a detection, and at an extremely non-solar abundance $m_{\rm Na}/m_{\rm Ca}>900$. The mass-loss rates and upper limits are tied to accretion in the white dwarfs, based on limiting cases for how the wind is captured, and compared with known cases of wind pollution from close M dwarf companions, which manifest in solar proportions between all elements detected. For wind captured in a Bondi-Hoyle flow, mass-loss limits $\dot M\lesssim 5\times10^{-17}$ M$_\odot$ yr$^{-1}$ are established for three L dwarfs, while for M dwarfs polluting their hosts, winds in the range $10^{-13} - 10^{-16}$ M$_\odot$ yr$^{-1}$ are found. The latter compares well with the $\dot M\sim 10^{-13} - 10^{-15}$ M$_\odot$ yr$^{-1}$ estimates obtained for nearby, isolated M dwarfs using Ly$\alpha$ to probe their astropsheres. These results demonstrate that white dwarfs are highly-sensitive stellar and substellar wind detectors, where further work on the actual captured wind flow is needed.

Authors:Samuel Beiler, Michael Cushing, Davy Kirkpatrick, Adam Schneider, Sagnick Mukherjee, Mark Marley

Abstract: We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06$-$540154.6 consists of low-resolution ($\lambda$/$\Delta\lambda$ $\sim$ 100) spectroscopy from 1$-$12 $\mu$m and three photometric points at 15, 18, and 21 $\mu$m. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H$_2$O, CH$_4$, CO, CO$_2$, and NH$_3$, including the previously unidentified $\nu_3$ band of NH$_3$ at 3 $\mu$m. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 $\mu$m, we measure a bolometric luminosity of $1.523\pm0.090\times10^{20}$ W. We determine a semi-empirical effective temperature estimate of $467^{+16}_{-18}$ K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having $T_{\mathrm{eff}}$=450 K, log $g$=3.25 [cm s$^{-2}$], [M/H]=$-0.3$. However, the low surface gravity implies an extremely low mass of 1 $M_{\rm{Jup}}$ and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.

Authors:Alison K. Young, Struan Stevenson, C. J. Nixon, Ken Rice

Abstract: Recent observations demonstrate that misalignments and other out-of-plane structures are common in protoplanetary discs. Many of these have been linked to a central host binary with an orbit that is inclined with respect to the disc. We present simulations of misaligned circumbinary discs with a range of parameters to gain a better understanding of the link between those parameters and the disc morphology in the wave-like regime of warp propagation that is appropriate to protoplanetary discs. The simulations confirm that disc tearing is possible in protoplanetary discs as long as the mass ratio, $\mu$, and disc-binary inclination angle, $i$, are not too small. For the simulations presented here this corresponds to $\mu > 0.1$ and $i \gtrsim 40^\circ$. For highly eccentric binaries, tearing can occur for discs with smaller misalignment. Existing theoretical predictions provide an estimate of the radial extent of the disc in which we can expect breaking to occur. However, there does not seem to be a simple relationship between the disc properties and the radius within the circumbinary disc at which the breaks appear, and furthermore the radius at which the disc breaks can change as a function of time in each case. We discuss the implications of our results for interpreting observations and suggest some considerations for modelling misaligned discs in the future.

Authors:William A. Burris, Carl Melis, Allen W. Shafter, Georgia V. Panopoulou, Edward L. Wright, John Della Costa

Abstract: We present optical and infrared imaging and spectroscopy of the R Coronae Borealis-type (R Cor Bor) star IRAS 00450+7401. Optical spectra further confirm its classification as a cool R Cor Bor system, having a hydrogen-deficient carbon star spectral sub-class of HdC5 or later. Mid-infrared spectroscopy reveals the typical ~8 um ``hump'' seen in other R Cor Bor stars and no other features. A modern-epoch spectral energy distribution shows bright emission from hot dust having Tdust>600 K. Historical infrared data reveal generally cooler dust color temperatures combined with long-term fading trends, but provide no discernible correlation between flux level and temperature. Investigating the most mid-infrared variable R Cor Bor stars found in IRAS, AKARI, and WISE data reveals similar fading trends, bursts that can show a factor of up to 10 change in flux density between epochs, and blackbody-fit dust color temperatures that span 400-1300 K. While some R Cor Bor stars such as IRAS 00450+7401 appear to undergo fade/burst cycles in the mid-infrared, significant gaps in temporal coverage prevent conclusively identifying any preferred timescale for their mid-infrared variability and circumstellar dust temperature changes.

Authors:E. Knudstrup, M. N. Lund, M. Fredslund Andersen, J. L. Rørsted, F. Pérez Hernández, F. Grundahl, P. L. Pallé, D. Stello, T. R. White, H. Kjeldsen, M. Vrard, M. L. Winther, R. Handberg, S. Simón-Díaz

Abstract: Fundamental stellar parameters such as mass and radius are some of the most important building blocks in astronomy, both when it comes to understanding the star itself and when deriving the properties of any exoplanet(s) they may host. Asteroseismology of solar-like oscillations allows us to determine these parameters with high precision. We investigate the solar-like oscillations of the red-giant-branch star $\gamma$ Cep A, which harbours a giant planet on a wide orbit. We did this by utilising both ground-based radial velocities from the SONG network and space-borne photometry from the NASA TESS mission. From the radial velocities and photometric observations, we created a combined power spectrum, which we used in an asteroseismic analysis to extract individual frequencies. We clearly identify several radial and quadrupole modes as well as multiple mixed, dipole modes. We used these frequencies along with spectroscopic and astrometric constraints to model the star, and we find a mass of $1.27^{+0.05}_{-0.07}$ M$_\odot$, a radius of $4.74^{+0.07}_{-0.08}$ R$_\odot$, and an age of $5.7^{+0.8}_{-0.9}$ Gyr. We then used the mass of $\gamma$ Cep A and our SONG radial velocities to derive masses for $\gamma$ Cep B and $\gamma$ Cep Ab of $0.328^{+0.009}_{-0.012}$ M$_\odot$ and $6.6^{+2.3}_{-2.8}$ M$_{\rm Jup}$, respectively.

Authors:M. Griggio Dipartimento di Fisica, Università di Ferrara INAF - Osservatorio Astronomico di Padova, M. Salaris Astrophysics Research Institute, Liverpool John Moores University INAF - Osservatorio Astronomico di Abruzzo, D. Nardiello INAF - Osservatorio Astronomico di Padova Aix Marseille Univ, LAM, L. R. Bedin INAF - Osservatorio Astronomico di Padova, S. Cassisi INAF - Osservatorio Astronomico di Abruzzo INFN - Sezione di Pisa, J. Anderson Space Telescope Science Institute

Abstract: We use new observations from the Canada-France-Hawaii Telescope to study the white dwarf cooling sequence of the open cluster M37, a cluster that displays an extended main sequence turn-off and, according to a recent photometric analysis, also a spread of initial chemical composition. By taking advantage of a first epoch collected in 1999 with the same telescope, we have been able to calculate proper motions for sources as faint as g ~ 26 (about ~ 6 magnitudes fainter than the Gaia limit), allowing us to separate cluster members from field stars. This has enabled us to isolate a sample of the white dwarf population of M37, reaching the end of the cooling sequence (at g ~ 23.5). The here-derived atlas and calibrated catalogue of the sources in the field of view is publicly released as supplementary on-line material. Finally, we present an exhaustive comparison of the white dwarf luminosity function with theoretical models, which has allowed us to exclude the age-spread scenario as the main responsible for the extended turnoff seen in the cluster colour-magnitude-diagram.

Authors:Michaela Brchnelova, Błażej Kuźma, Fan Zhang, Andrea Lani, Stefaan Poedts

Abstract: COCONUT is a global coronal magnetohydrodynamic model recently developed. In order to achieve robustness and fast convergence to steady-state, several assumptions have been made during its development, such as prescribing filtered photospheric magnetic maps for representing the magnetic field in the lower corona. This filtering leads to smoothing and lower magnetic field values at the inner boundary, resulting in an unrealistically high plasma beta.In this paper, we examine the effects of prescribing such filtered magnetograms and formulate a method for achieving more realistic plasma beta values without losing computational performance. We demonstrate the effects of the highly pre-processed magnetic maps and the resulting high plasma beta on the features in the domain. Then, in our new approach, we shift the inner boundary to 2 Rs and preserve the prescribed highly filtered magnetic map. This effectively reduces the prescribed plasma beta and leads to a more realistic setup. The method is applied on a magnetic dipole, a minimum (2008) and a maximum (2012) solar activity case, to demonstrate its effects. The results obtained with the proposed approach show significant improvements in the resolved density and radial velocity profiles, and far more realistic values of the plasma \{beta} at the boundary and inside the computational domain. This is also demonstrated via synthetic white light imaging and with the validation against tomography. The computational performance comparison shows similar convergence to a limit residual on the same grid when compared to the original setup. Considering that the grid can be further coarsened with this new setup, the operational performance can be additionally increased if needed. The newly developed method is thus deemed as a good potential replacement of the original setup for operational purposes.

Authors:Yuka Terada, Hauyu Baobab Liu, David Mkrtichian, Jinshi Sai, Mihoko Konishi, Ing-Guey Jiang, Takayuki Muto, Jun Hashimoto, Motohide Tamura

Abstract: The powerful, high-energy magnetic activities of young stars play important roles in the magnetohydrodynamics in the innermost parts of the protoplanetary disks. In addition, the associated UV and X-ray emission dictates the photochemistry; moreover, the corona activities can affect the atmosphere of a newborn extra-solar planet. How the UV and X-ray photons are generated, and how they illuminate the disks, are not well understood. Here we report the analyses of the optical and infrared (OIR) photometric monitoring observations and the high angular-resolution centimeter band images of the low-mass (M1 type) pre-main sequence star, DM Tau. We found that the OIR photometric light curves present periodic variations, which is consistent with that the host young star is rotating in the same direction as the natal disk and is hosting at least one giant cold spot. In addition, we resolved that the ionized gas in the DM Tau disk is localized, and its spatial distribution is varying with time. All the present observations can be coherently interpreted, if the giant cold spot is the dominant anisotropic UV and/or X-ray source that illuminates the ambient cone-like region. These results indicate that a detailed theoretical model of the high-energy protostellar emission is essential in the understanding of the space weather around the extra-solar planets and the origin of life.

Authors:Yuxi Lu, Victor See, Louis Amard, Ruth Angus, Sean P. Matt

Abstract: The importance of the existence of a radiative core in generating a solar-like magnetic dynamo is still unclear. Analytic models and magnetohydrodynamic simulations of stars suggest the thin layer between a star's radiative core and its convective zone can produce shearing that reproduces key characteristics of a solar-like dynamo. However, recent studies suggest fully and partially convective stars exhibit very similar period-activity relations, hinting that dynamos generated by stars with and without radiative cores hold similar properties. Here, using kinematic ages, we discover an abrupt change in the stellar spin-down law across the fully convective boundary. We found that fully convective stars exhibit a higher angular momentum loss rate, corresponding to a torque that is $\sim$ 2.25 times higher for a given angular velocity than partially convective stars around the fully convective boundary. This requires a dipole field strength that is larger by a factor of $\sim$2.5, a mass loss rate that is $\sim$4.2 times larger, or some combination of both of those factors. Since stellar-wind torques depend primarily on large-scale magnetic fields and mass loss rates, both of which derive from magnetic activity, the observed abrupt change in spin-down law suggests that the dynamos of partially and fully convective stars may be fundamentally different

Authors:Xingyao Chen, Eduard P. Kontar, Nicolina Chrysaphi, Peijin Zhang, Vratislav Krupar, Sophie Musset, Milan Maksimovic, Natasha L. S. Jeffrey, Francesco Azzollini, Antonio Vecchio

Abstract: Interplanetary solar radio type III bursts provide the means for remotely studying and tracking energetic electrons propagating in the interplanetary medium. Due to the lack of direct radio source imaging, several methods have been developed to determine the source positions from space-based observations. Moreover, none of the methods consider the propagation effects of anisotropic radio-wave scattering, which would strongly distort the trajectory of radio waves, delay their arrival times, and affect their apparent characteristics. We investigate the source positions and directivity of an interplanetary type III burst simultaneously observed by Parker Solar Probe, Solar Orbiter, STEREO, and Wind and compare the results of applying the intensity fit and timing methods with ray-tracing simulations of radio-wave propagation with anisotropic density fluctuations. The simulation calculates the trajectories of the rays, their time profiles at different viewing sites, and the apparent characteristics for various density fluctuation parameters. The results indicate that the observed source positions are displaced away from the locations where emission is produced, and their deduced radial distances are larger than expected from density models. This suggests that the apparent position is affected by anisotropic radio-wave scattering, which leads to an apparent position at a larger heliocentric distance from the Sun. The methods to determine the source positions may underestimate the apparent positions if they do not consider the path of radio-wave propagation and incomplete scattering at a viewing site close to the intrinsic source position.

Authors:Jean-François Le Borgne

Abstract: NSV 14264 and NSV 14172 are suspected to be variable stars of RR Lyr type (Brun, 1964). They were observed during three nights in October 2018 with a 25cm diameter telescope. These observations completed by ASAS-SN survey data bring to the conclusion that these two stars are not RR Lyraes but constant stars in the limit of the precision of the present photometry. The analysis of GAIA data allows to say that NSV 14264 is a main sequence dwarf similar to the Sun but that NSV 14172 is a yellow giant star located in the HR diagram at the limit between RR Lyraes and CW cepheids; however, it does not pulsate with significant amplitude.

Authors:Izumi Hachisu, Mariko Kato

Abstract: YZ Ret is the first X-ray flash detected classical nova, and is also well observed in optical, X-ray, and gamma-ray. We propose a comprehensive model that explains the observational properties. The white dwarf mass is determined to be $\sim 1.33 ~M_\odot$ that reproduces multiwavelength light curves of YZ Ret, from optical, X-ray, and to gamma-ray. We show that a shock is naturally generated far outside the photosphere because winds collide with themselves. The derived lifetime of shock explains some of the temporal variations of emission lines. The shocked shell significantly contributes to the optical flux in the nebular phase. The decline trend of shell emission in the nebular phase is close to $\propto t^{-1.75}$ and the same as the universal decline law of classical novae, where $t$ is the time from the outburst.

Authors:J. I. Peralta, M. C. Vieytes, A. M. P. Mendez, D. M. Mitnik

Abstract: Aims. We tested the new atomic model using atmospheric models of stars of different spectral types: the Sun (dG2), HD22049 (dK2, Epsilon Eridani), GJ 832 (dM2), and GJ 581 (dM3). Methods. We used new Breit-Pauli distorted-wave (DW) multiconfiguration calculations, which proved to be relevant for many transitions in the mid-infrared (MIR) range. The new atomic model of Mg I includes the following: i) recomputed ECS data through the DW method, including the superlevels. ii) For the nonlocal thermodynamic equilibrium (NLTE) population calculations, 5676 theoretical transitions were added (3001 term-to-term). iii) All of these improvements were studied in the Sun and the stars listed above. Results. The Mg distribution between ionization states for stars with different effective temperatures was compared. For the Sun and Epsilon Eridani, Mg II predominates with more than 95 %, while for GJ 832 and GJ 581, Mg I represents more than 72 % of the population. Moreover, in the latter stars, the amount of Mg forming molecules in their atmosphere is at least two orders of magnitude higher. Regarding the NLTE population, a noticeable lower variability in the departure coefficients was found, indicating a better population coupling for the new model. Comparing the synthetic spectrum calculated with the older and new Mg I atomic model, these results show minimal differences in the visible range but they are stronger in the IR for all of the stars. This aspect should be considered when using lines from this region as indicators. Nevertheless, some changes in the spectral type were found, also emphasizing the need to test the atomic models in different atmospheric conditions. The most noticeable changes occurred in the FUV and NUV, obtaining a higher flux for the new atomic model regardless of the spectral type.

Authors:Adam Moss University of Oklahoma, Mukremin Kilic University of Oklahoma, P. Bergeron Université de Montréal, Megan Firgard University of Oklahoma, Warren Brown Smithsonian Astrophysical Observatory

Abstract: We present our findings on the spectral analysis of seven magnetic white dwarfs that were presumed to be double degenerates. We obtained time-resolved spectroscopy at the Gemini Observatory to look for evidence of binarity or fast rotation. We find three of our targets have rotation periods of less than an hour based on the shifting positions of the Zeeman-split H$\alpha$ components: 13, 35, and 39 min, and we find one more target with a ~hour long period that is currently unconstrained. We use offset dipole models to determine the inclination, magnetic field strength, and dipole offset of each target. The average surface field strengths of our fast rotators vary by 1-2 MG between different spectra. In all cases, the observed absorption features are too shallow compared to our models. This could be due to extra flux from a companion for our three low-mass targets, but the majority of our sample likely requires an inhomogeneous surface composition. Including an additional magnetic white dwarf with similar properties presented in the literature, we find that 5 of the 8 targets in this sample show field variations on minute/hour timescales. A crystallization driven dynamo can potentially explain the magnetic fields in three of our targets with masses above $0.7~M_{\odot}$ but another mechanism is still needed to explain their rapid rotation. We suggest that rapid rotation or low-masses point to binary evolution as the likely source of magnetism in 7 of these 8 targets.

Authors:Ingrid Pelisoli, T. R. Marsh, David A. H. Buckley, I. Heywood, Stephen. B. Potter, Axel Schwope, Jaco Brink, Annie Standke, P. A. Woudt, S. G. Parsons, M. J. Green, S. O. Kepler, James Munday, A. D. Romero, E. Breedt, A. J. Brown, V. S. Dhillon, M. J. Dyer, P. Kerry, S. P. Littlefair, D. I. Sahman, J. F. Wild

Abstract: White dwarf stars are the most common stellar fossils. When in binaries, they make up the dominant form of compact object binary within the Galaxy and can offer insight into different aspects of binary formation and evolution. One of the most remarkable white dwarf binary systems identified to date is AR Scorpii (henceforth AR Sco). AR Sco is composed of an M-dwarf star and a rapidly-spinning white dwarf in a 3.56-hour orbit. It shows pulsed emission with a period of 1.97 minutes over a broad range of wavelengths, which led to it being known as a white dwarf pulsar. Both the pulse mechanism and the evolutionary origin of AR Sco provide challenges to theoretical models. Here we report the discovery of the first sibling of AR Sco, J191213.72-441045.1 (henceforth J1912-4410), which harbours a white dwarf in a 4.03-hour orbit with an M-dwarf and exhibits pulsed emission with a period of 5.30 minutes. This discovery establishes binary white dwarf pulsars as a class and provides support for proposed formation models for white dwarf pulsars.

Authors:Dóra Tarczay-Nehéz, László Molnár, Attila Bódi, Róbert Szabó

Abstract: Ultra-low amplitude (ULA) and strange mode Cepheids are thought to be pulsating variable stars that are near to or are at the edges of the classical instability strip. Until now, a few dozen such variable star candidates have been found both in the Large Magellanic Cloud and the Milky Way. In this present work, we studied six ULA Cepheid candidates in the Milky Way, identified by Szab\'o et al. (2009) using CoRoT and 2MASS data. In order to identify their positions in the period--luminosity and color--magnitude diagrams, we used the Gaia DR3 parallax and brightness data of each star to calculate their reddening-free absolute magnitudes and distances. Furthermore, we calculated the Fourier parameters (e.g., period and amplitude) of the light variations based on CoRoT and TESS measurements, and established the long-term phase shifts for four out of six stars. Based on the results, we conclude that none of the six ULA Cepheid candidates are pulsating variable stars, but rather rotation-induced variable stars (rotational spotted and $\alpha^2$~Canum Venaticorum variables) that are either bluer or fainter than Cepheids would be.

Authors:Noam Soker Technion, Israel

Abstract: I compared with each other and with observations three energy sources to power intermediate luminosity optical transients (ILOTs) and conclude that only jets can power bright ILOTs with rapidly rising lightcurves. I present an expression for the power of the jets that a main sequence secondary star launches as it enters a common envelope evolution (CEE) with a primary giant star. The expression includes the Keplerian orbital period on the surface of the primary star, its total envelope mass, and the ratio of masses. I show that the shock that the secondary star excites in the envelope of the primary star cannot explain bright peaks in the lightcurves of ILOTs, and that powering by jets does much better in accounting for rapidly rising, about 10 days and less, peaks in the lightcurves of ILOTs than the recombination energy of the ejected mass. I strengthen previous claims that jets powered the Great Eruption of Eta Carinae, which was a luminous variable major eruption, and the luminous red novae (LRNe) V838 Mon and V1309 Scorpii. I therefore predict that the ejecta (nebula) of V1309 Scorpii will be observed in a decade or two to be bipolar. My main conclusion is that only jets can power a bright peak with a short rising time of ILOTs (LRNe) at CEE formation.

Authors:Thomas Hackman, Oleg Kochukhov, Mariangela Viviani, Jörn Warnecke, Maarit J. Korpi-Lagg, Jyri J. Lehtinen

Abstract: Zeeman-Doppler imaging (ZDI) is used to reconstruct the surface magnetic field of late-type stars from high resolution spectropolarimetric observations. The results are usually described in terms of characteristics of the field topology, i.e. poloidality vs. toroidality and axi-symmetry vs. non-axisymmetry in addition to the field strength. We want to test how well these characteristics are preserved when applying the ZDI method on simulated data, i.e. how accurately the field topology is preserved and to what extent stellar parameters influence the reconstruction. We use published magnetic field data from direct numerical MHD simulations. These have variable rotation rates, and hence represent different levels of activity, of an otherwise Sun-like setup. Our ZDI reconstruction is based on spherical harmonics expansion. By comparing the original values to those of the reconstructed images, we study the ability to reconstruct the surface magnetic field in terms of various characteristics of the field. The main large-scale features are reasonably well recovered, but the strength of the recovered magnetic field is just a fraction of the original input. The quality of the reconstruction shows clear correlations with the data quality. Furthermore, there are some spurious dependencies between stellar parameters and the characteristics of the field. Our study uncovers some limits of ZDI. Firstly, the recovered field strength will generally be lower than the "real" value as smaller structures with opposite polarities will be blurred in the inversion. Secondly, the axi-symmetry is overestimated. The poloidality vs. toroidality is better recovered. The reconstruction works better for a stronger field and faster rotation velocity. Still, the ZDI method works surprisingly well even for a weaker field and slow rotation, provided the data has a high signal-to-noise and good rotation phase coverage.

Authors:M. A. Gómez-Muñoz, R. Vázquez, L. Sabin, L. Olguín, P. F. Guillén, S. Zavala, R. Michel

Abstract: We investigated the origin of the Planetary Nebula (PN) M 1-16 using narrow band optical imaging, and high and low resolution optical spectra to perform a detailed morphokinematic and chemical studies. M 1-16 is revealed to be a multipolar PN that predominantly emits in [O III] in the inner part of the nebula and [N II] in the lobes. A novel spectral unsharp masking technique was applied to the position-velocity maps (PVs) to reveal a set of multiple structures at the centre of M 1-16 spanning radial velocities from $-40km\,s{-1}$ to $20km\,s{-1}$, with respect to the systemic velocity . The morphokinematic model indicates that the deprojected velocity of the lobe outflows are $\geq100km\,s{-1}$, and particularly the larger lobes and knots have a deprojected velocity of $\simeq350km\,s{-1}$; the inner ellipsoidal component has a deprojected velocity of $\simeq29km\,s{-1}$. A kinematical age of $\sim$8700yr has been obtained from the model assuming an homologous velocity expansion law and a distance of 6.2$\pm$1.9kpc. The chemical analysis indicates that M 1-16 is a Type I PN with a central star of PN (CSPN) mass in the range of $\simeq0.618-0.713$M$\odot$ and an initial mass for the progenitor star between 2.0 and 3.0M$\odot$ (depending on metalicity). An $T_\mathrm{eff}\simeq140\,000$K and log($L/{\rm L}_{\odot})$=2.3 was estimated using the 3MdB photoionization models to reproduce the ionisation stage of the PN. All these results lead us to suggest that M 1-16 is an evolved PN, contrary to the scenario of proto-PN suggested in previous studies. We propose that the mechanism responsible for the morphology of M 1-16 is related to the binary (or multiple star) evolution scenario.

Authors:Viktória Fröhlich, Zsolt Regály, József Vinkó

Abstract: Since the discovery of the first double neutron star (DNS) system, the number of these exotic binaries has reached fifteen. Here we investigate a channel of DNS formation in binary systems with components above the mass limit of type II supernova explosion (SN II), i.e. 8 MSun. We apply a spherically symmetric homologous envelope expansion model to account for mass loss, and follow the dynamical evolution of the system numerically with a high-precision integrator. The first SN occurs in a binary system whose orbital parameters are pre-defined, then, the homologous expansion model is applied again in the newly formed system. Analysing 1 658 880 models we find that DNS formation via subsequent SN II explosions requires a fine-tuning of the initial parameters. Our model can explain DNS systems with a separation greater than 2.95 au. The eccentricity of the DNS systems spans a wide range thanks to the orbital circularisation effect due to the second SN II explosion. The eccentricity of the DNS is sensitive to the initial eccentricity of the binary progenitor and the orbital position of the system preceding the second explosion. In agreement with the majority of the observations of DNS systems, we find the system centre-of mass velocities to be less than 60 km/s. Neutron stars that become unbound in either explosion gain a peculiar velocity in the range of 0.02 - 240 km/s. In our model, the formation of tight DNS systems requires a post-explosion orbit-shrinking mechanism, possibly driven by the ejected envelopes.

Authors:M. Griggio Dipartimento di Fisica, Università di Ferrara INAF - Osservatorio Astronomico di Padova, M. Salaris Astrophysics Research Institute, Liverpool John Moores University INAF - Osservatorio Astronomico di Abruzzo, L. R. Bedin INAF - Osservatorio Astronomico di Padova, S. Cassisi INAF - Osservatorio Astronomico di Abruzzo INFN - Sezione di Pisa

Abstract: Our recent multi-band photometric study of the colour width of the lower main sequence of the open cluster M37 has revealed the presence of a sizeable initial chemical composition spread in the cluster. If initial chemical composition spreads are common amongst open clusters, this would have major implications for cluster formation models and the foundation of the chemical tagging technique. Here we present a study of the unevolved main sequence of the open cluster M38, employing Gaia DR3 photometry and astrometry, together with newly acquired Sloan photometry. We have analysed the distribution of the cluster's lower main sequence stars with a differential colour-colour diagram made of combinations of Gaia and Sloan magnitudes, like in the study of M37. We employed synthetic stellar populations to reproduce the observed trend of M38 stars in this diagram, and found that the observed colour spreads can be explained simply by the combined effect of differential reddening across the face of the cluster and the presence of unresolved binaries. There is no need to include in the synthetic sample a spread of initial chemical composition as instead necessary to explain the main sequence of M37. Further photometric investigations like ours, as well as accurate differential spectroscopic analyses on large samples of open clusters, are necessary to understand whether chemical abundance spreads are common among the open cluster population.

Authors:Thore Espedal Moe, Tiago M. D. Pereira, Flavio Calvo, Jorrit Leenaarts

Abstract: The shapes of Stokes profiles contain much information about the atmospheric conditions that produced them. However, a variety of different atmospheric structures can produce very similar profiles. Thus, it is important for proper interpretation of observations to have a good understanding of how the shapes of Stokes profiles depend on the underlying atmosphere. An excellent tool in this regard is forward modeling, i.e. computing and studying synthetic spectra from realistic simulations of the solar atmosphere. Modern simulations routinely produce several hundred thousand spectral profiles per snapshot. With such numbers, it becomes necessary to use automated procedures in order to organize the profiles according to their shape. Here we illustrate the use of two complementary methods, k-means and k-Shape, to cluster similarly shaped profiles, and demonstrate how the resulting clusters can be combined with knowledge of the simulation's atmosphere to interpret spectral shapes. We generate synthetic Stokes profiles for the Ca II 854.2 nm line using the Multi3D code from a Bifrost simulation snapshot. We then apply the k-means and k-Shape clustering techniques to group the profiles together according to their shape. We show and compare the classes of profile shapes we retrieve from applying both k-means and k-Shape to our synthetic intensity spectra. We then show the structure of the underlying atmosphere for two particular classes of profile shapes retrieved by the clustering, and demonstrate how this leads to an interpretation for the formation of those profile shapes. Furthermore, we apply both methods to the subset of our profiles containing the strongest Stokes V signals, and demonstrate how k-Shape can be qualitatively better than k-means at retrieving complex profile shapes when using a small number of clusters.

Authors:Zsófia Bora, József Vinkó, Réka Könyves-Tóth

Abstract: We infer initial masses of the synthesized radioactive nickel-56 in a sample of recent Type Ia supernovae applying a new formalism introduced recently by Khatami & Kasen (2019). It is shown that the nickel masses we derive do not differ significantly from previous estimates based on the traditional Arnett-model. We derive the $\beta$ parameter for our sample SNe and show that these are consistent with the fiducial value of $\sim 1.6$ given by Khatami & Kasen (2019) from SN Ia hydrodynamical simulations.

Authors:László Molnár, Meridith Joyce, Shing-Chi Leung

Abstract: The recent pre-print by Saio et al. 2023 argues that the supergiant Betelgeuse is already undergoing carbon burning, based on the assumption that all of its light variations are caused by radial pulsations. However, the angular diameter measurements of the star are in conflict with the stellar radius required by their models, as we show in this note. We discuss the feasibility that the Great Dimming was caused by constructive mode interference using long-term brightness measurements and comment on differences in modeling frameworks adopted in Saio et al. 2023 vs Joyce et al. 2020.

Authors:M. Mittag, J. H. M. M. Schmitt, K. -P. Schröder

Abstract: We analyse the relation between the activity cycle length and the Rossby number and collected a sample of 44 main sequence stars with well-known activity cycle periods and rotation periods. We find a linear behaviour in the double-logarithmic relation between the Rossby number and cycle period. The bifurcation into a long and a short period branch is clearly real but it depends, empirically, on the colour index B-V, indicating a physical dependence on effective temperature and position on the main sequence. Furthermore, there is also a correlation between cycle length and convective turnover time with the relative depth of the convection zone. Based on this, we derive empirical relations between cycle period and Rossby number, and for the short period cycle branch relations, we estimate a scatter of the relative deviation between 14% and 28% on the long-period cycle branch. With these relations, we obtain a good match with the 10.3 yr period for the well known 11-year solar Schwabe cycle and a long-period branch value of 104 yr for the Gleissberg cycle of the Sun. Finally, we suggest that the cycles on the short-period branch appear to be generated in the deeper layers of the convective zone, while long-period branch cycles seem to be related to fewer deep layers in that zone. We show that for a broader B-V range, the Rossby number is a more suitable parameter for universal relation with cycle-rotation than just the rotation period alone. As proof, we demonstrate that our empirical stellar relations are consistent with the 11-year solar Schwabe cycle, in contrast to earlier studies using just the rotation period in their relations. Previous studies have tried to explain the cycle position of the Sun in the cycle-rotation presentation via other kinds of dynamo, however, in our study, no evidence is found that would suggest another type of dynamo for the Sun and other stars.

Authors:Amit Kashi

Abstract: We simulate the hydrodynamics of the wind flow in the B[e] supergiant binary system GG~Carinae and obtain the mass accretion rate onto the secondary and the observed lightcurve. We find an inhomogeneous Bondi-Hoyle-Lyttleton accretion into a curved accretion tail, and confirm that the accretion rate is modulated along the orbit, with a maximum close to periastron. We show that the accretion itself cannot account for the periodical variation in brightness. Instead, we explain the observed variation in the light curve with absorption by the accretion tail. Our results are in general agreement with previously derived stellar masses, orbital parameters, and the system orientation, but imply that the B[e] supergiant is more luminous. We find an effect related to the orbital motion of the two stars, in which the accretion tail is cut by the primary and we term it the Lizard Autotomy Effect. As part of the effect, the primary is self accreting wind that it ejected earlier. The Lizard Autotomy Effect creates an outwardly expanding spiral shell made up of broken segments. We suggest that such a tail exists in other B[e] supergiant systems and can be the source of the circumstellar material observed in such systems. The accretion also forms a disc around the secondary near periastron that later vanishes. We suggest that the formation of such a disc can launch jets that account for the bipolar structure observed around some B[e] supergiants.

Authors:Ayan Biswas, Barnali Das, Poonam Chandra, Gregg A. Wade, Matthew E. Shultz, Francesco Cavallaro, Veronique Petit, Patrick A. Woudt, Evelyne Alecian

Abstract: Magnetic fields are extremely rare in close, hot binaries, with only 1.5\% of such systems known to contain a magnetic star. The eccentric $\epsilon$ Lupi system stands out in this population as the only close binary in which both stars are known to be magnetic. We report the discovery of strong, variable radio emission from $\epsilon$ Lupi using the upgraded Giant Metrewave Radio Telescope (uGMRT) and the MeerKAT radio telescope.The light curve exhibits striking, unique characteristics including sharp, high-amplitude pulses that repeat with the orbital period, with the brightest enhancement occurring near periastron. The characteristics of the light curve point to variable levels of magnetic reconnection throughout the orbital cycle, making $\epsilon$ Lupi the first known high-mass, main sequence binary embedded in an interacting magnetosphere. We also present a previously unreported enhancement in the X-ray light curve obtained from archival XMM-Newton data. The stability of the components' fossil magnetic fields, the firm characterization of their relatively simple configurations, and the short orbital period of the system make $\epsilon$ Lupi an ideal target to study the physics of magnetospheric interactions. This system may thus help us to illuminate the exotic plasma physics of other magnetically interacting systems such as moon-planet, planet-star, and star-star systems including T Tauri binaries, RS CVn systems, and neutron star binaries.

Authors:G. Cozzo, J. Reid, P. Pagano, F. Reale, A. W. Hood

Abstract: A possible key element for large-scale energy release in the solar corona is an MHD kink instability in a single twisted magnetic flux tube. An initial helical current sheet fragments in a turbulent way into smaller-scale sheets, similarly to a nanoflare storm. As the loop expands in the radial direction during the relaxation process, an unstable loop can disrupt nearby stable loops and trigger an MHD avalanche. Exploratory investigations have been conducted in previous works with relatively simplified loop configurations. Here, we address a more realistic environment that comprehensively accounts for most of the physical effects involved in a stratified atmosphere, typical of an active region. The question is whether the avalanche process will be triggered, with what timescales, and how it will develop, as compared with the original, simpler approach. Three-dimensional MHD simulations describe the interaction of magnetic flux tubes, which have a stratified atmosphere, including chromospheric layers, the thin transition region to the corona, and the related transition from high-beta to low-beta regions. The model also includes the effects of thermal conduction and of optically thin radiation. Our simulations address the case where one flux tube among a few is twisted at the footpoints faster than its neighbours. We show that this flux tube becomes kink unstable first, in conditions in agreement with those predicted by analytical models. It rapidly involves nearby stable tubes, instigating significant magnetic reconnection and dissipation of energy as heat. The heating determines the development of chromospheric evaporation, while the temperature rises up to about 10 MK, close to microflares observations. This work confirms that avalanches are a viable mechanism for the storing and release of magnetic energy in plasma confined in closed coronal loops, as a result of photospheric motions.

Authors:Mihailo M. Martinovic, Kristopher G. Klein

Abstract: Linear theory is a well developed framework for characterizing instabilities in weakly collisional plasmas, such as the solar wind. In the previous instalment of this series, we analyzed ~1.5M proton and alpha particle Velocity Distribution Functions (VDFs) observed by Helios I and II to determine the statistical properties of the standard instability parameters such as the growth rate, frequency, the direction of wave propagation, and the power emitted or absorbed by each component, as well as to characterize their behavior with respect to the distance from the Sun and collisional processing. In this work, we use this comprehensive set of instability calculations to train a Machine Learning algorithm consisting of three interlaced components that: 1) predict if an interval is unstable from observed VDF parameters; 2) predict the instability properties for a given unstable VDF; and 3) classify the type of the unstable mode. We use these methods to map the properties in multi-dimensional phase space to find that the parallel-propagating, proton-core-induced Ion Cyclotron mode dominates the young solar wind, while the oblique Fast Magnetosonic mode regulates the proton beam drift in the collisionally old plasma.

Authors:Dong Li, Xianyong Bai, Hui Tian, Jiangtao Su, Zhenyong Hou, Yuanyong Deng, Kaifan Ji, Zongjun Ning

Abstract: We investigate the traveling kink oscillation triggered by a solar flare on 2022 September 29. The observational data is mainly measured by the Solar Upper Transition Region Imager (SUTRI), the Atmospheric Imaging Assembly (AIA), and the Spectrometer/Telescope for Imaging X-rays (STIX). The transverse oscillations with apparent decaying in amplitudes, which are nearly perpendicular to the oscillating loop, are observed in passbands of SUTRI 465 A, AIA 171 A, and 193 A. The decaying oscillation is launched by a solar flare erupted closely to one footpoint of coronal loops, and then it propagates along several loops. Next, the traveling kink wave is evolved to a standing kink oscillation. To the best of our knowledge, this is the first report of the evolution of a traveling kink pulse to a standing kink wave along coronal loops. The standing kink oscillation along one coronal loop has a similar period of about 6.3 minutes at multiple wavelengths, and the decaying time is estimated to about 9.6-10.6 minutes. Finally, two dominant periods of 5.1 minutes and 2.0 minutes are detected in another oscillating loop, suggesting the coexistence of the fundamental and third harmonics.

Authors:Jun Chen, Xin Cheng, Bernhard Kliem, Mingde Ding

Abstract: The violent disruption of the coronal magnetic field is often observed to be restricted to the low corona, appearing as a confined eruption. The possible causes of the confinement remain elusive. Here, we model the eruption of a magnetic flux rope in a quadrupolar active region, with the parameters set such that magnetic X-lines exist both below and above the rope. This facilitates the onset of magnetic reconnection in either place but with partly opposing effects on the eruption. The lower reconnection initially adds poloidal flux to the rope, increasing the upward hoop force and supporting the rise of the rope. However, when the flux of the magnetic side lobes enters the lower reconnection, the flux rope is found to separate from the reconnection site and the flux accumulation ceases. At the same time, the upper reconnection begins to reduce the poloidal flux of the rope, decreasing its hoop force; eventually this cuts the rope completely. The relative weight of the two reconnection processes is varied in the model, and it is found that their combined effect and the tension force of the overlying field confine the eruption if the flux ratio of the outer to the inner polarities exceeds a threshold, which is about 1.3 for our Cartesian box and chosen parameters. We hence propose that external reconnection between an erupting flux rope and overlying flux can play a vital role in confining eruptions.

Authors:S. P. Järvinen, S. Hubrig, R. Jayaraman, A. Cikota, M. Schöller

Abstract: Studies of magnetic fields in the most evolved massive stars, the Wolf-Rayet stars, are of special importance because they are progenitors of certain types of supernovae. The first detection of a magnetic field of the order of a few hundred Gauss in the WN7 star WR55, based on a few FORS2 low-resolution spectropolarimetric observations, was reported in 2020. In this work we present new FORS2 observations allowing us to detect magnetic and spectroscopic variability with a period of 11.90 h. No significant frequencies were detected in TESS and ASAS-SN photometric observations. Importantly, magnetic field detections are achieved currently only in two Wolf-Rayet stars, WR6 and WR55, both showing the presence of corotating interacting regions.

Authors:J. Magdolen, A. Dobrotka, M. Orio, J. Mikołajewska, A. Vanderburg, B. Monard, R. Aloisi, P. Bezák

Abstract: AIMS: We investigated the optical variability of the symbiotic binary FN Sgr, with photometric monitoring during $\simeq$55 years and with a high-cadence Kepler light curve lasting 81 days. METHODS: The data obtained in the V and I bands were reduced with standard photometric methods. The Kepler data were divided into subsamples and analyses with the Lomb-Scargle algorithm. RESULTS: The V and I band light curves showed a phenomenon never before observed with such recurrence in any symbiotic system, namely short outbursts, starting between orbital phase 0.3 and 0.5 and lasting about a month, with a fast rise and a slower decline, and amplitude of 0.5-1 mag. In the Kepler light curve we discovered three frequencies with sidebands. We attribute a stable frequency of 127.5 d$^{-1}$ (corresponding to an 11.3 minutes period) to the white dwarf rotation. We suggest that this detection probably implies that the white dwarf accretes through a magnetic stream, like in intermediate polars. The small outbursts may be ascribed to the stream-disc interaction. Another possibility is that they are due to localized thermonuclear burning, perhaps confined by the magnetic field, like recently inferred in intermediate polars, albeit on different timescales. We measured also a second frequency around 116.9 d$^{-1}$ (corresponding to about 137 minutes), which is much less stable and has a drift. It may be due to rocky detritus around the white dwarf, but it is more likely to be caused by an inhomogeneity in the accretion disk. Finally, there is a third frequency close to the first one that appears to correspond to the beating between the rotation and the second frequency.

Authors:C. J. Nelson, F. Auchère, R. Aznar Cuadrado, K. Barczynski, E. Buchlin, L. Harra, D. M. Long, S. Parenti, H. Peter, U. Schühle, C. Schwanitz, P. Smith, L. Teriaca, C. Verbeeck, A. N. Zhukov, D. Berghmans

Abstract: Localised transient EUV brightenings, sometimes named `campfires', occur throughout the quiet-Sun. However, there are still many open questions about such events, in particular regarding their temperature range and dynamics. In this article, we aim to determine whether any transition region response can be detected for small-scale EUV brightenings and, if so, to identify whether the measured spectra correspond to any previously reported bursts in the transition region, such as Explosive Events (EEs). EUV brightenings were detected in a ~29.4 minute dataset sampled by Solar Orbiter's Extreme Ultraviolet Imager on 8 March 2022 using an automated detection algorithm. Any potential transition region response was inferred through analysis of imaging and spectral data sampled through coordinated observations conducted by the Interface Region Imaging Spectrograph (IRIS). EUV brightenings display a range of responses in IRIS slit-jaw imager (SJI) data. Some events have clear signatures in the Mg II and Si IV SJI filters, whilst others have no discernible counterpart. Both extended and more complex EUV brightenings are found to, sometimes, have responses in IRIS SJI data. Examples of EUI intensities peaking before, during, and after their IRIS counterparts were found in lightcurves constructed co-spatial to EUV brightenings. Importantly, therefore, it is likely that not all EUV brightenings are driven in the same way, with some seemingly being magnetic reconnection driven and others not. A single EUV brightening occurred co-spatial to the IRIS slit, with its spectra matching the properties of EEs. EUV brightenings is a term used to describe a range of small-scale event in the solar corona. The physics responsible for all EUV brightenings is likely not the same and, therefore, more research is required to assess their importance towards global questions in the field, such as coronal heating.

Authors:Leandro G. Althaus, Alejandro H. Córsico, María E. Camisassa, Santiago Torres, Pilar Gil-Pons, Alberto Rebassa-Mansergas, Roberto Raddi

Abstract: We employ the La Plata stellar evolution code, LPCODE, to compute the first set of constant rest-mass carbon-oxygen ultra-massive white dwarf evolutionary sequences for masses higher than 1.29 Msun that fully take into account the effects of general relativity on their structural and evolutionary properties. In addition, we employ the LP-PUL pulsation code to compute adiabatic g-mode Newtonian pulsations on our fully relativistic equilibrium white dwarf models. We find that carbon-oxygen white dwarfs more massive than 1.382 Msun become gravitationally unstable with respect to general relativity effects, being this limit higher than the 1.369 Msun we found for oxygen-neon white dwarfs. As the stellar mass approaches the limiting mass value, the stellar radius becomes substantially smaller compared with the Newtonian models. Also, the thermo-mechanical and evolutionary properties of the most massive white dwarfs are strongly affected by general relativity effects. We also provide magnitudes for our cooling sequences in different passbands. Finally, we explore for the first time the pulsational properties of relativistic ultra-massive white dwarfs and find that the period spacings and oscillation kinetic energies are strongly affected in the case of most massive white dwarfs. We conclude that the general relativity effects should be taken into account for an accurate assessment of the structural, evolutionary, and pulsational properties of white dwarfs with masses above 1.30 Msun.

Authors:Marie Van de Sande, Catherine Walsh, Tom J. Millar

Abstract: Observations of the outflows of asymptotic giant branch (AGB) stars continue to reveal their chemical and dynamical complexity. Spherical asymmetries, such as spirals and disks, are prevalent and thought to be caused by binary interaction with a (sub)stellar companion. Furthermore, high density outflows show evidence of dust-gas interactions. The classical chemical model of these outflows - a gas-phase only, spherically symmetric chemical kinetics model - is hence not appropriate for a majority of observed outflows. We have included several physical and chemical advancements step-by-step: a porous density distribution, dust-gas chemistry, and internal UV photons originating from a close-by stellar companion. Now, we combine these layers of complexity into the most chemically and physically advanced chemical kinetics model of AGB outflows to date. By varying over all model parameters, we obtain a holistic view of the outflow's composition and how it (inter)depends on the different complexities. A stellar companion has the largest influence, especially when combined with a porous outflow. We compile sets of gas-phase molecules that trace the importance of dust-gas chemistry and allow us to infer the presence of a companion and porosity of the outflow. This shows that our new chemical model can be used to infer physical and chemical properties of specific outflows, as long as a suitable range of molecules is observed.

Authors:Patrick R. Behr, Kevin France, Alexander Brown, Girish Duvvuri, Jacob L. Bean, Zachory Berta-Thompson, Cynthia Froning, Yamila Miguel, J. Sebastian Pineda, David Wilson, Allison Youngblood

Abstract: X-ray through infrared spectral energy distributions (SEDs) are essential for understanding a star's effect on exoplanet atmospheric composition and evolution. We present a catalog of panchromatic SEDs, hosted on the Barbara A. Mikulski Archive for Space Telescopes (MAST), for 11 exoplanet hosting stars which have guaranteed JWST observation time as part of the ERS or GTO programs but have no previous UV characterization. The stars in this survey range from spectral type F4-M6 (0.14-1.57 M$_\odot$), rotation periods of ~4-132 days, and ages of approximately 0.5-11.4 Gyr. The SEDs are composite spectra using data from the Chandra X-ray Observatory and XMM-Newton, the Hubble Space Telescope, BT-Settl stellar atmosphere models, and scaled spectra of proxy stars of similar spectral type and activity. From our observations, we have measured a set of UV and X-ray fluxes as indicators of stellar activity level. We compare the chromospheric and coronal activity indicators of our exoplanet-hosting stars to the broader population of field stars and find that a majority of our targets have activity levels lower than the average population of cool stars in the solar neighborhood. This suggests that using SEDs of stars selected from exoplanet surveys to compute generic exoplanet atmosphere models may underestimate the typical host star's UV flux by an order of magnitude or more, and consequently, that the observed population of exoplanetary atmospheres receive lower high-energy flux levels than the typical planet in the solar neighborhood.

Authors:A. Afanasyev, Y. Fan, M. Kazachenko, M. Cheung

Abstract: We present first results of the hybrid data-driven magnetofrictional (MF) and data-constrained magnetohydrodynamic (MHD) simulations of solar active region NOAA 11158, which produced an X-class flare and coronal mass ejection on 2011 February 15. First, we apply the MF approach to build the coronal magnetic configuration corresponding to the SDO/HMI photospheric magnetograms by using the JSOC PDFI SS electric field inversions at the bottom boundary of the simulation domain. We then use the pre-eruptive MF state at about 1.5 hour before the observed X-class flare as the initial state for the MHD simulation, assuming a stratified polytropic solar corona. The MHD run shows that the initial magnetic configuration containing twisted magnetic fluxes and a 3D magnetic null point is out of equilibrium. We find the eruption of a complex magnetic structure consisting of two magnetic flux ropes, as well as the development of flare ribbons, with their morphology being in good agreement with observations. We conclude that the combination of the data-driven MF and data-constrained MHD simulations is a useful practical tool for understanding the 3D magnetic structures of real solar ARs that are unobservable otherwise.

Authors:Jouni J. Takalo

Abstract: We study the solar flare index (SFI) for the solar cycles 18\,--\,24. We find that SFI has deeper Gnevyshev gap (GG) in its first principal component than other atmospheric parameters. The GG is extremely clear especially in the even cycles. The GG of the SFI appears about a half year later as a drop in the interplanetary magnetic field near the Earth and in the geomagnetic Ap-index. The instantaneous response of the magnetic field to solar flares, however, shows about two to three days after the eruption as a high, sharp peak in the cross-correlation of the SFI and Ap-index and as a lower peak in SFI vs. IMF B cross-correlation. We confirm these rapid responses using superposed-epoch analysis. The most active flare cycles during 1944-2020 are the Cycles 19 and 21. The Cycle 18 has very strong SFI days as much as Cycle 22, but it has least nonzero SFI days in the whole interval. Interestingly Cycle 20 can be compared to the Cycles 23 and 24 in its low flare activity, although it locates between the most active SFI cycles.

Authors:Jérôme Bétrisey, Gaël Buldgen, Daniel R. Reese, Martin Farnir, Marc-Antoine Dupret, Saniya Khan, Marie-Jo Goupil, Patrick Eggenberger, Georges Meynet

Abstract: Asteroseismic modelling will be part of the pipeline of the PLATO mission and will play a key role in the mission precision requirements on stellar mass, radius and age. It is therefore crucial to compare how current modelling strategies perform, and discuss the limitations and remaining challenges for PLATO, such as the so-called surface effects, the choice of physical ingredients, and stellar activity. In this context, we carried out a systematic study of the impact of surface effects on the estimation of stellar parameters. In this work, we demonstrated how combining a mean density inversion with a fit of frequencies separation ratios can efficiently damp the surface effects and achieve precise and accurate stellar parameters for ten Kepler LEGACY targets, well within the PLATO mission requirements. We applied and compared two modelling approaches, directly fitting the individual frequencies, or coupling a mean density inversion with a fit of the ratios, to six synthetic targets with a patched 3D atmosphere from Sonoi et al. (2015) and ten actual targets from the LEGACY sample. The fit of the individual frequencies is unsurprisingly very sensitive to surface effects and the stellar parameters tend to be biased, which constitutes a fundamental limit to both accuracy and precision. In contrast, coupling a mean density inversion and a fit of the ratios efficiently damps the surface effects, and allows us to get both precise and accurate stellar parameters. The average statistical precision of our selection of LEGACY targets with this second strategy is 1.9% for the mass, 0.7% for the radius, and 4.1% for the age, well within the PLATO requirements. Using the mean density in the constraints significantly improves the precision of the mass, radius and age determinations, on average by 20%, 33%, and 16%, respectively.

Authors:Charles A. Bowesman, Irina I. Mizus, Nikolay F. Zobov, Oleg L. Polyansky, Janos Sarka, Bill Poirier, Marco Pezzella, Sergei N. Yurchenko, Jonathan Tennyson

Abstract: New MiZo line lists are presented for the D$_2$H$^+$ and D$_3^+$ isotopologues of H$_3^+$. These line lists plus the existing H$_3^+$ MiZATeP and the Sochi H$_2$D$^+$ line lists are updated using empirical energy levels generated using the MARVEL procedure for H$_3^+$, H$_2$D$^+$ and D$_2$H$^+$, and effective Hamiltonian energies for D$_3^+$ for which there is significantly less laboratory data available. These updates allow accurate frequencies for far infrared lines for these species to be predicted. Assignments of the energy levels of H$_3^+$ and D$_3^+$ are extended using a combination of high accuracy variational calculations and analysis of transition intensities. All line lists are made available via www.exomol.com.

Authors:J. F. Drake, S. D. Bale, M. Swisdak, N. E. Raouafi, M. Velli

Abstract: The role of interchange reconnection as a drive mechanism for the solar wind is explored by solving the global magnetic-field-aligned equations describing wind acceleration. Boundary conditions in the low corona, including a reconnection-driven Alfv\'enic outflow and associated heating differ from previous models. Additional heating of the corona associated with Alfv\'en waves or other MHD turbulence, which has been the foundation of many earlier models, is neglected. For this simplified model a sufficient condition for interchange reconnection to overcome gravity to drive the wind is derived. The combination of Alfv\'enic ejection and reconnection-driven heating yields a minimum value of the Alfv\'en speed of the order of 350-400$km/s$ that is required to drive the wind. Recent evidence based on Parker Solar Probe (PSP) observations suggests that this threshold is typically exceeded in the coronal holes that are the source regions of the fast wind. On the other hand, since reconnection in the coronal environment is predicted to have a bursty character, the magnitude of reconnection outflows can be highly variable. The consequence is a highly non-uniform wind in which in some regions the velocity increases sharply to super-Alfv\'enic values while in adjacent regions the formation of an asymptotic wind fails. A simple model is constructed to describe the turbulent mixing of these highly-sheared super-Alfv\'enic flows that suggests these flows are the free-energy source of the Alfv\'enic turbulence and associated switchbacks that have been documented in the PSP data in the near coronal environment. The global wind profiles are presented and benchmarked with Parker Solar Probe (PSP) observations at 12 solar radii.

Authors:Elspeth K. H. Lee, Xianyu Tan, Shang-Min Tsai

Abstract: The atmospheres of brown dwarfs have been long observed to exhibit a multitude of non-equilibrium chemical signatures and spectral variability across the L, T and Y spectral types. We aim to investigate the link between the large-scale 3D atmospheric dynamics and time-dependent chemistry in the brown dwarf regime, and to assess its impact on spectral variability. We couple the miniature kinetic chemistry module `mini-chem' to the Exo-FMS general circulation model (GCM). We then perform a series of idealised brown dwarf regime atmospheric models to investigate the dynamical 3D chemical structures produced by our simulations. The GCM output is post-processed using a 3D radiative-transfer model to investigate hemisphere-dependent spectral signatures and rotational variability. Our results show the expected strong non-equilibrium chemical behaviour brought on by vertical mixing as well as global spacial variations due to zonal flows. Chemical species are generally globally homogenised, showing variations of $\pm$10\% or less, dependent on pressure level, and follow the dynamical structures present in the atmosphere. However, we find localised storm regions and eddies can show higher contrasts, up to $\pm$100\%, in mixing ratio compared to the background global mean. This initial study represents another step in understanding the connection between three-dimensional atmospheric flows in brown dwarfs and their rich chemical inventories.

Authors:Noam Dori Technion, Israel, Ealeal Bear Technion, Israel, Noam Soker Technion, Israel

Abstract: We find that the convective motion in the envelopes of red supergiant (RSG) stars supplies a non-negligible stochastic angular momentum to the mass that a secondary star accretes in a common envelope evolution (CEE), such that jets that the secondary star launches wobble. The orbital motion of the secondary star in a CEE and the density gradient in the envelope impose a non-zero angular momentum to the accreted mass with a constant direction parallel to the orbital angular momentum. From one-dimensional stellar evolution simulations with the numerical code \textsc{mesa} we find that the stochastic convection motion in the envelope of RSG stars adds a stochastic angular momentum component with an amplitude that is about 0.1-1 times that of the constant component due to the orbital motion. We mimic a CEE of the RSG star by removing envelope mass at a high rate and by depositing energy into its envelope. The stochastic angular momentum implies that the accretion disk around the secondary star (which we do not simulate), and therefore the jets that it launches, wobble with angles of up to tens of degrees with respect to the orbital angular momentum axis. This wobbling makes it harder for jets to break out from the envelope and can shape small bubbles in the ejecta that compress filaments that appear as arcs in the ejected nebula, i.e., in planetary nebulae when the giant is an asymptotic giant branch star.

Authors:L. M. Rebull, R. L. Anderson III, G. Hall, J. D. Kirkpatrick, X. Koenig, C. E. Odden, B. Rodriguez, R. Sanchez, B. Senson, V. Urbanowski, M. Austin, K. Blood, E. Kerman, J. Long, N. Roosa

Abstract: IC 417 is in the Galactic Plane, and likely part of the Aur OB2 association; it is ~2 kpc away. Stock 8 is one of the densest cluster constituents; off of it to the East, there is a 'Nebulous Stream' (NS) that is dramatic in the infrared (IR). We have assembled a list of literature-identified young stellar objects (YSOs), new candidate YSOs from the NS, and new candidate YSOs from IR excesses. We vetted this list via inspection of the images, spectral energy distributions (SEDs), and color-color/color-magnitude diagrams. We placed the 710 surviving YSOs and candidate YSOs in ranked bins, nearly two-thirds of which have more than 20 points defining their SEDs. The lowest-ranked bins include stars that are confused, or likely carbon stars. There are 503 in the higher-ranked bins; half are SED Class III, and $\sim$40\% are SED Class II. Our results agree with the literature in that we find that the NS and Stock 8 are at about the same distance as each other (and as the rest of the YSOs), and that the NS is the youngest region, with Stock 8 a little older. We do not find any evidence for an age spread within the NS, consistent with the idea that the star formation trigger came from the north. We do not find that the other literature-identified clusters here are as young as either the NS or Stock 8; at best they are older than Stock 8, and they may not all be legitimate clusters.

Authors:A. Perdomo García, N. Vitas, E. Khomenko, M. Collados, C. Allende Prieto, I. Hubeny, Y. Osorio

Abstract: Context. Realistic 3D time-dependent simulations of stellar near-surface convection employ the opacity binning method for efficient and accurate computation of the radiative energy exchange. The method provides several orders of magnitude of speed-up, but its implementation includes a number of free parameters. Aims. Our aim is to evaluate the accuracy of the opacity binning method as a function of the choice of these free parameters. Methods. The monochromatic opacities computed with the SYNSPEC code are used to construct opacity distribution function (ODF) that is then verified through detailed comparison with the results of the ATLAS code. The opacity binning method is implemented with the SYNSPEC opacities for four representative cool main-sequence stellar spectral types (F3V, G2V, K0V, and M2V). Results. The ODFs from SYNSPEC and ATLAS show consistent results for the opacity and bolometric radiative energy exchange rate Q in case of the F, G, and K -- type stars. Significant differences, coming mainly from the molecular line lists, are found for the M -- type star. It is possible to optimise a small number of bins to reduce the deviation of the results coming from the opacity grouping with respect to the ODF for the F, G, and K -- type stars. In the case of the M -- type star, the inclusion of splitting in wavelength is needed in the grouping to get similar results, with a subsequent increase in computing time. In the limit of a large number of bins, the deviation for all the binning configurations tested saturates and the results do not converge to the ODF solution. Due to this saturation, the Q rate cannot be improved by increasing the number of bins to more than about 20 bins. The more effective strategy is to select the optimal location of fewer bins.

Authors:Jeffrey W. Reep, Vladimir S. Airapetian

Abstract: Recent irradiance measurements from numerous heliophysics and astrophysics missions including SDO, GOES, Kepler, TESS, Chandra, XMM-Newton, and NICER have provided critical input in understanding the physics of the most powerful transient events on the Sun and magnetically active stars, solar and stellar flares. The light curves of flare events from the Sun and stars show remarkably similar shapes, typically with a sharp rise and protracted decay phase. The duration of solar and stellar flares has been found to be correlated with the intensity of the event in some wavelengths, such as white light, but not in other wavelengths, such as soft X-rays, but it is not evident why this is the case. In this study, we use a radiative hydrodynamics code to examine factors affecting the duration of flare emission at various wavelengths. The duration of a light curve depends on the temperature of the plasma, the height in the atmosphere at which the emission forms, and the relative importance of cooling due to radiation, thermal conduction, and enthalpy flux. We find that there is a clear distinction between emission that forms low in the atmosphere and responds directly to heating, and emission that forms in the corona, indirectly responding to heating-induced chromospheric evaporation, a facet of the Neupert effect. We discuss the implications of our results to a wide range of flare energies.

Authors:Arianna Dwomoh, Evan B. Bauer

Abstract: The polluted white dwarf (WD) system SDSS J122859.93+104032.9 (SDSS J1228) shows variable emission features interpreted as originating from a solid core fragment held together against tidal forces by its own internal strength, orbiting within its surrounding debris disk. Estimating the size of this orbiting solid body requires modeling the accretion rate of the polluting material that is observed mixing into the WD surface. That material is supplied via sublimation from the surface of the orbiting solid body. The sublimation rate can be estimated as a simple function of the surface area of the solid body and the incident flux from the nearby hot WD. On the other hand, estimating the accretion rate requires detailed modeling of the surface structure and mixing in the accreting WD. In this work, we present MESA WD models for SDSS J1228 that account for thermohaline instability and mixing in addition to heavy element sedimentation to accurately constrain the sublimation and accretion rate necessary to supply the observed pollution. We derive a total accretion rate of $\dot M_{\rm acc}=1.8\times 10^{11}\,\rm g\,s^{-1}$, several orders of magnitude higher than the $\dot M_{\rm acc}=5.6\times 10^{8}\,\rm g\,s^{-1}$ estimate obtained in earlier efforts. The larger mass accretion rate implies that the minimum estimated radius of the orbiting solid body is r$_{\rm{min}}$ = 72 km, which, although significantly larger than prior estimates, still lies within upper bounds (a few hundred km) for which the internal strength could no longer withstand tidal forces from the gravity of the WD.

Authors:L. Gehrig, E. Gaidos, M. Güdel

Abstract: We investigate the influence of an accretion disk on the angular momentum (AM) evolution of young M dwarfs, which parameters govern the AM distribution after the disk phase, and whether this leads to a mass-independent distribution of SAM. We find that above an initial rate $\Dot{M}_\mathrm{crit} \sim 10^{-8}~\Msolpyr$ accretion "erases" the initial SAM of M dwarfs during the disk lifetime, and stellar rotation converges to values of SAM that are largely independent of initial conditions. For stellar masses $> 0.3~\mathrm{M_\odot}$, we find that observed initial accretion rates $\Dot{M}_\mathrm{init}$ are comparable to or exceed $\Dot{M}_\mathrm{crit}$. Furthermore, stellar SAM after the disk phase scales with the stellar magnetic field strength as a power-law with an exponent of $-1.1$. For lower stellar masses, $\Dot{M}_\mathrm{init}$ is predicted to be smaller than $\Dot{M}_\mathrm{crit}$ and the initial conditions are imprinted in the stellar SAM after the disk phase. To explain the observed mass-independent distribution of SAM, the stellar magnetic field strength has to range between 20~G and 500~G (700~G and 1500~G) for a 0.1~$\mathrm{M_\odot}$ (0.6~$\mathrm{M_\odot}$) star. These values match observed large-scale magnetic field measurements of young M~dwarfs and the positive relation between stellar mass and magnetic field strength agrees with a theoretically-motivated scaling relation. The scaling law between stellar SAM, mass, and the magnetic field strength is consistent for young stars, where these parameters are constrained by observations. Due to the very limited number of available data, we advocate for efforts to obtain more such measurements. Our results provide new constraints on the relation between stellar mass and magnetic field strength and can be used as initial conditions for future stellar spin models, starting after the disk phase. (shortened)

Authors:Po-Ya Wang Institute of Astronomy, NTHU Department of Physics, NTHU, Tomotsugu Goto Institute of Astronomy, NTHU Department of Physics, NTHU, Simon C. -C. Ho Research School of Astronomy and Astrophysics, ANU, Yu-Wei Lin Institute of Astronomy, NTHU Department of Physics, NTHU, Cossas K. -W. Wu Institute of Astronomy, NTHU Department of Physics, NTHU, Chih-Teng Ling Institute of Astronomy, NTHU, Tetsuya Hashimoto Department of Physics, NCHU, Seong Jin Kim Institute of Astronomy, NTHU, Tiger Y. -Y. Hsiao Center of Astrophysical Science, JHU

Abstract: We present a distant T$-$type brown dwarf candidate at $\approx2.55$ kpc discovered in the Cosmic Evolution Early Release Science (CEERS) fields by James Webb Space Telescope (JWST) NIRCam. In addition to the superb sensitivity, we utilised 7 filters from JWST in near-IR and thus is advantageous in finding faint, previously unseen brown dwarfs. From the model spectra in new JWST/NIRCam filter wavelengths, the selection criteria of F115W-F277W$<$-0.8 and F277W-F444W$>$1.1 were chosen to target the spectrum features of brown dwarfs having temperatures from 500K to 1300K. Searching through the data from Early Release Observations (ERO) and Early Release Science (ERS), we find 1 promising candidate in the CEERS field. The result of SED fitting suggested an early T spectral type with a low effective temperature of T$_\text{eff}\approx$1300K, the surface gravity of $\log{g}\approx5.25\text{cm s}^{-2}$, and an eddy diffusion parameter of logK$_{zz}\approx7\text{cm}^2 \text{s}^{-1}$, which indicates an age of $\approx$1.8Gyr and a mass of $\approx0.05$M$_{\odot}$. In contrast to typically found T$-$dwarf within several hundred parsecs, the estimated distance of the source is $\approx2.55$kpc, showing the JWST's power to extend the search to a much larger distance.

Authors:Burak Ulas

Abstract: We present an image classification algorithm using deep learning convolutional neural network architecture, which classifies the morphologies of eclipsing binary systems based on their light curves. The algorithm trains the machine with light curve images generated from the observational data of eclipsing binary stars in contact, detached and semi-detached morphologies, whose light curves are provided by Kepler, ASAS and CALEB catalogues. The structure of the architecture is explained, the parameters of the network layers and the resulting metrics are discussed. Our results show that the algorithm, which is selected among 132 neural network architectures, estimates the morphological classes of an independent validation dataset, 705 real data, with an accuracy of 92%.

Authors:H. Bakke, L. Frogner, L. Rouppe van der Voort, B. V. Gudiksen, M. Carlsson

Abstract: Nanoflare heating through small-scale magnetic reconnection events is one of the prime candidates to explain heating of the solar corona. However, direct signatures of nanoflares are difficult to determine, and unambiguous observational evidence is still lacking. Numerical models that include accelerated electrons, and can reproduce flaring conditions, are essential in understanding how low-energetic events act as a heating mechanism of the corona, and how such events are able to produce signatures in the spectral lines that can be detected through observations. We investigate the effects of accelerated electrons in synthetic spectra from a 3D radiative magnetohydrodynamics simulation to better understand small-scale heating events and their impact on the solar atmosphere. We synthesised the chromospheric Ca II and Mg II lines and the transition region Si IV resonance lines from a quiet Sun numerical simulation that includes accelerated electrons. We calculated the contribution function to the intensity to better understand how the lines are formed, and what factors are contributing to the detailed shape of the spectral profiles. The synthetic spectra are highly affected by variations in temperature and vertical velocity. Beam heating exceeds conductive heating at the heights where the spectral lines form, indicating that the electrons should contribute to the heating of the lower atmosphere and hence affect the line profiles. However, we find that it is difficult to determine specific signatures from the non-thermal electrons due to the complexity of the atmospheric response to the heating in combination with the relatively low energy output (~1e21 erg/s). Still, our results contribute to the understanding of small-scale heating events in the solar atmosphere, and give further guidance to future observations.

Authors:P. Kohutova, P. Antolin, M. Szydlarski, M. Carlsson

Abstract: Oscillations are abundant in the solar corona. Coronal loop oscillations are typically studied using highly idealised models of magnetic flux tubes. In order to improve our understanding of coronal oscillations, it is necessary to consider the effect of realistic magnetic field topology and density structuring. We analyse the damping of coronal oscillations using a self-consistent 3D radiation-MHD simulation of the solar atmosphere spanning from the convection zone into the corona, the associated oscillation dissipation and heating, and finally the physical processes responsible for the damping and dissipation. The simulated corona formed in such a model does not depend on any prior assumptions about the shape of the coronal loops. We find that the bundle of magnetic loops shows damped transverse oscillations in response to perturbations in two separate instances with oscillation periods of 177 s and 191 s, velocity amplitudes of 10 km/s and 16 km/s and damping times of 176 s and 198 s, respectively. The coronal oscillations lead to the development of velocity shear in the simulated corona resulting in the formation of vortices seen in the velocity field caused by the Kelvin-Helmholtz instability, contributing to the damping and dissipation of the transverse oscillations. The oscillation parameters and evolution observed are in line with the values typically seen in observations of coronal loop oscillations. The dynamic evolution of the coronal loop bundle suggests the models of monolithic and static coronal loops with constant lengths might need to be re-evaluated by relaxing the assumption of highly idealised waveguides.

Authors:D. D. Hendriks, R. G. Izzard

Abstract: We present the software package binary_c-python which provides a convenient and easy-to-use interface to the binary_c framework, allowing the user to rapidly evolve individual systems and populations of stars. binary_c-python is available on Pip and on GitLab. binary_c-python contains many useful features to control and process the output of binary_c, like by providing binary_c-python with logging statements that are dynamically compiled and loaded into binary_c. Moreover, we have recently added standardised output of events like Roche-lobe overflow or double compact-object formation to binary_c, and automatic parsing and managing of that output in binary_c-python. binary_c-python uses multiprocessing to utilise all the cores on a particular machine, and can run populations with HPC cluster workload managers like HTCondor and Slurm, allowing the user to run simulations on large computing clusters. We provide documentation that is automatically generated based on docstrings and a suite of Jupyter notebooks. These notebooks consist of technical tutorials on how to use binary_c-python and use-case scenarios aimed at doing science. Much of binary_c-python is covered by unit tests to ensure reliability and correctness, and the test coverage is continually increased as the package is improved.

Authors:D. Pamos Ortega, G. M. Mirouh, A. García Hernández, J. C. Suárez Yanes, S. Barceló Forteza

Abstract: Aims. The main goal of this work is to date young open clusters using $\delta$ Sct stars. Seismic indices such as the large separation and the frequency at maximum power can help to constrain the models to better characterise the stars. We propose a reliable method to identify some radial modes, which gives us greater confidence in the constrained models. Methods. We extract the frequency content of a sample of $\delta$ Sct stars belonging to the same open cluster. We estimate the low-order large separation by means of different techniques and the frequency at maximum power for each member of the sample. We use a grid of models built with the typical parameters of $\delta$ Sct stars, including mass, metallicity and rotation as independent variables, and determine the oscillation modes. We select the observed frequencies whose ratios match those of the models. Once we find a range of radial modes matching the observed frequencies, mainly the fundamental mode, we add it to the other seismic parameters to derive the stellar age. Assuming star groups have similar chemistry and age, we estimate their mean age by computing a weighted probability density function fit to the age distribution of the seismically constrained models. Results. We estimate the age of Trumpler 10 to be $30_{-20}{+30}$ Myr, and that of Praesepe to be $580 \pm 230$ Myr. In this latter case, we find two apparent populations of $\delta$ Sct stars in the same cluster, one at $510 \pm 140$ Myr and another at $890 \pm 140$ Myr. This may be due to two different formation events, different rotational velocities of the members in our sample of stars (as rapid rotation may modify the observed large separation), or to membership of unresolved binary systems.

Authors:L. Cacciapuoti, E. Macias, A. J. Maury, C. J. Chandler, N. Sakai, Ł. Tychoniec, S. Viti, A. Natta, M. De Simone, A. Miotello, C. Codella, C. Ceccarelli, L. Podio, D. Fedele, D. Johnstone, Y. Shirley, B. J. Liu, E. Bianchi, Z. E. Zhang, J. Pineda, L. Loinard, F. Ménard, U. Lebreuilly, R. S. Klessen, P. Hennebelle, S. Molinari, L. Testi, S. Yamamoto

Abstract: Early dust grain growth in protostellar envelopes infalling on young discs has been suggested in recent studies, supporting the hypothesis that dust particles start to agglomerate already during the Class 0/I phase of young stellar objects (YSOs). If this early evolution were confirmed, it would impact the usually assumed initial conditions of planet formation, where only particles with sizes $\lesssim 0.25 \mu$m are usually considered for protostellar envelopes. We aim to determine the maximum grain size of the dust population in the envelope of the Class 0/I protostar L1527 IRS, located in the Taurus star-forming region (140 pc). We use Atacama Large millimetre/sub-millimetre Array (ALMA) and Atacama Compact Array (ACA) archival data and present new observations, in an effort to both enhance the signal-to-noise ratio of the faint extended continuum emission and properly account for the compact emission from the inner disc. Using observations performed in four wavelength bands and extending the spatial range of previous studies, we aim to place tight constraints on the spectral ($\alpha$) and dust emissivity ($\beta$) indices in the envelope of L1527 IRS. We find a rather flat $\alpha \sim$ 3.0 profile in the range 50-2000 au. Accounting for the envelope temperature profile, we derive values for the dust emissivity index, 0.9 < $\beta$ < 1.6, and reveal a tentative, positive outward gradient. This could be interpreted as a distribution of mainly ISM-like grains at 2000 au, gradually progressing to (sub-)millimetre-sized dust grains in the inner envelope, where at R=300 au, $\beta$ = 1.1 +/- 0.1. Our study supports a variation of the dust properties in the envelope of L1527 IRS. We discuss how this can be the result of in-situ grain growth, dust differential collapse from the parent core, or upward transport of disc large grains.

Authors:Atila Poro, Eduardo Fernández Lajús, Mohammad Madani, Golshan Sabbaghian, Farshid Nasrollahzadeh, Faezeh Jahediparizi

Abstract: The short-period AP Dor eclipsing binary's first in-depth and multiband photometric solutions are presented. We made use of our eight nights of ground-based at a southern hemisphere observatory, and twelve sectors of TESS observations. We extracted eight and 1322 minima from our observations and TESS, respectively. We suggested a new linear ephemeris based on the trend of orbital period variations using the Markov chain Monte Carlo (MCMC) approach. The PHysics Of Eclipsing BinariEs (PHOEBE) Python code and the MCMC approach were used for the light curve analysis. This system did not require a starspot for the light curve solutions. We calculated the absolute parameters of the system using Gaia DR3 parallax method. The orbital angular momentum (J_0) of the AP Dor indicates that this system is located in a region of contact binaries. According to our results, this system is an overcontact binary system with a mass ratio of 0.584, a fillout factor of 48%, and an inclination of 53deg. The positions of AP Dor stars on the Hertzsprung-Russell (HR) diagram are represented.

Authors:Nived Vilangot Nhalil, Juie Shetye, J. Gerry Doyle

Abstract: New instrumental and telescopes covering the optical and ultra-violet spectral regions have revealed a range of small-scale dynamic features, many which may be related. For example, the range of spicule-like features hints towards a spectrum of features and not just two types; however, direct observational evidence in terms of tracking spicules across multiple wavelengths are needed in order to provide further insight into the dynamics of the Sun's outer atmosphere. This paper uses H $\alpha$ data obtained with the CRisp Imaging SpectroPolarimeter instrument on the Swedish 1-m Solar Telescope, and in the transition region using the Interface Region Imaging Spectrograph with the SJI 1400 {\AA} channel plus spectral data via the Si IV 1394 {\AA} line to track spicules termed Rapid Blue-shifted Excursions (RBEs). The RBEs as seen in the H $\alpha$ blue-wing images presented here can be sub-divided into two categories; a single or multi-threaded feature. Based on the H $\alpha$ spectra, the features can be divided into events showing broadening and line core absorption, events showing broadening and line core emission, events with a pure blue shifted H $\alpha$ profile without any absorption in the red wing, broadened line profile with the absorption in the blue stronger compared to the red wing. From the RBE-like events which have a Si IV 1394 {\AA} line profile, 78% of them show a Si IV line flux increase. Most of these features show a second broadened Si IV component which is slightly blue-shifted.

Authors:Renae E. Wall, Mukremin Kilic, P. Bergeron, Nathan D. Leiphart

Abstract: We present a detailed model atmosphere analysis of 14001 DA white dwarfs from the Montreal White Dwarf Database with ultraviolet photometry from the GALEX mission. We use the 100 pc sample, where the extinction is negligible, to demonstrate that there are no major systematic differences between the best-fit parameters derived from optical only data and the optical + UV photometry. GALEX FUV and NUV data improve the statistical errors in the model fits, especially for the hotter white dwarfs with spectral energy distributions that peak in the UV. Fitting the UV to optical spectral energy distributions also reveals UV-excess or UV-deficit objects. We use two different methods to identify outliers in our model fits. Known outliers include objects with unusual atmospheric compositions, strongly magnetic white dwarfs, and binary white dwarfs, including double degenerates and white dwarf + main-sequence systems. We present a list of 89 newly identified outliers based on GALEX UV data; follow-up observations of these objects will be required to constrain their nature. Several current and upcoming large scale spectroscopic surveys are targeting $>10^5$ white dwarfs. In addition, the ULTRASAT mission is planning an all-sky survey in the NUV band. A combination of the UV data from GALEX and ULTRASAT and optical data on these large samples of spectroscopically confirmed DA white dwarfs will provide an excellent opportunity to identify unusual white dwarfs in the solar neighborhood.

Authors:Mariko Kato, Izumi Hachisu

Abstract: CN Cha is a slow symbiotic nova characterized by a three-years-long optical flat peak followed by a rapid decline. We present theoretical light curves for CN Cha, based on hydrostatic approximation, and estimate the white dwarf (WD) mass to be $\sim 0.6 ~M_\odot$ for a low metal abundance of Z = 0.004. This kind of flat peak novae are border objects between classical novae having a sharp optical peak and extremely slow novae, the evolutions of which are too slow to be recognized as a nova outburst in human timescale. Theoretically, there are two types of nova envelope solutions, static and optically-thick wind, in low mass WDs ($\lesssim 0.7 ~M_\odot$). Such a nova outburst begins first in a hydrostatic manner, and later it could change to an optically-thick wind evolution due to perturbation by the companion star in the nova envelope. Multiple peaks are a reflection of the relaxation process of transition. CN Cha supports our explanation on the difference between long-lasted flat peak novae like CN Cha and multiple peak novae like V723 Cas, because the companion star is located far outside, and does not perturb, the nova envelope in CN Cha.

Authors:C. Quintero Noda, E. Khomenko, M. Collados, B. Ruiz Cobo, R. Gafeira, N. Vitas, M. Rempel, R. J. Campbell, A. Pastor Yabar, H. Uitenbroek, D. Orozco Suárez

Abstract: In this work, we study the accuracy that can be achieved when inferring the atmospheric information from realistic numerical magneto-hydrodynamic simulations that reproduce the spatial resolution we will obtain with future observations made by the 4m class telescopes DKIST and EST. We first study multiple inversion configurations using the SIR code and the Fe I transitions at 630 nm until we obtain minor differences between the input and the inferred atmosphere in a wide range of heights. Also, we examine how the inversion accuracy depends on the noise level of the Stokes profiles. The results indicate that when the majority of the inverted pixels come from strongly magnetised areas, there are almost no restrictions in terms of the noise, obtaining good results for noise amplitudes up to 1$\times10^{-3}$ of $I_c$. At the same time, the situation is different for observations where the dominant magnetic structures are weak, and noise restraints are more demanding. Moreover, we find that the accuracy of the fits is almost the same as that obtained without noise when the noise levels are on the order of 1$\times10^{-4}$of $I_c$. We, therefore, advise aiming for noise values on the order of or lower than 5$\times10^{-4}$ of $I_c$ if observers seek reliable interpretations of the results for the magnetic field vector reliably. We expect those noise levels to be achievable by next-generation 4m class telescopes thanks to an optimised polarisation calibration and the large collecting area of the primary mirror.

Authors:Charlotte O. G. Waterfall, Silvia Dalla, Mike S. Marsh, Timo Laitinen, Adam Hutchinson

Abstract: The forecasting of solar energetic particles (SEPs) is a prominent area of space weather research. Numerous forecasting models exist that predict SEP event properties at proton energies <100MeV. One of these models is the SPARX system, a physics-based forecasting tool that calculates >10MeV and >60MeV flux profiles within minutes of a flare being detected. This work describes SPARX-H, the extension of SPARX to forecast SEP events above 300MeV . SPARX-H predicts fluxes in three high energy channels up to several hundred MeV. Correlations between SEP peak flux and peak intensity of the associated solar flare are seen to be weak at high energies, but improved when events are grouped based on the field polarity during the event. Initial results from this new high energy forecasting tool are presented here and the applications of high energy forecasts are discussed. Additionally, the new high energy version of SPARX is tested on a set of historic SEP events. We see that SPARX-H performs best when predicting peak fluxes from events with source locations in well-connected regions, where many large SEP events tend to originate.

Authors:Richard Monier, E. Niemczura, D. W. Kurtz, S. Rappaport, D. M. Bowman, Simon J. Murphy, Yveline Lebreton, Remko Stuik, Morgan Deal, Thibault Merle, Tolgahan Kılıçoğlu, Marwan Gebran, Ewen Le Ster

Abstract: We report on a detailed abundance study of six bright, mostly southern, slowly rotating late B stars: HD~1279 (B8III), HD~99803 (B9V), HD~123445 (B9V), HD~147550 (B9V), HD~171961 (B8III) and HD~202671 (B5II/III), hitherto reported as normal stars. We compare them to the two classical HgMn stars $\mu$ Lep and $\beta$ Scl and to the superficially normal star, $\nu$ Cap. In the spectra of the six stars, the \ion{Hg}{2} line at 3984 \AA\ line is clearly seen and numerous lines of P, Ti, Mn, Fe, Ga, Sr, Y, and Zr appear to be strong absorbers. A comparison of newly acquired and archival spectra of these objects with a grid of synthetic spectra for selected unblended lines reveals large overabundances of P, Ti, Cr, Mn, Sr, Y, Zr, Ba, Pt and Hg and underabundances of He, Mg, Sc and Ni. The effective temperatures, surface gravities, low projected rotational velocities and the peculiar abundance patterns of the six investigated stars show that they are new chemically peculiar stars, mostly new HgMn stars, and are reclassified as such. The evolutionary status of these stars has been inferred and their ages and masses estimated. The two most massive objects, HD~1279 and HD~202671, might have evolved away from the main-sequence recently, the other stars are main-sequence objects. HD~99803A is a sharp lined HgMn star with grazing eclipses; from TESS and MASCARA photometry we determine an orbital period of $P_{\rm orb} = 26.12022 \pm 0.00004$\,d.

Authors:Hiroki Kawashimo, Ryo Sawada, Yudai Suwa, Takashi J. Moriya, Ataru Tanikawa, Nozomu Tominaga

Abstract: Nuclear reactions are key to our understanding of stellar evolution, particularly the $^{12}\rm{C}\left({\alpha},{\gamma}\right)^{16}\!\rm{O}$ rate, which is known to significantly influence the lower and upper ends of the black hole (BH) mass distribution due to pair-instability supernovae (PISNe). However, these reaction rates have not been sufficiently determined. We use the $\texttt{MESA}$ stellar evolution code to explore the impact of uncertainty in the $^{12}\rm{C}\left({\alpha},{\gamma}\right)^{16}\!\rm{O}$ rate on PISN explosions, focusing on nucleosynthesis and explosion energy by considering the high resolution of the initial mass. Our findings show that the mass of synthesized radioactive nickel ($^{56}{\rm Ni}$) and the explosion energy increase with $^{12}\rm{C}\left({\alpha},{\gamma}\right)^{16}\!\rm{O}$ rate for the same initial mass, except in the high-mass edge region. With a high (about twice the $\texttt{STARLIB}$ standard value) rate, the maximum amount of nickel produced falls below 70 $M_\odot$, while with a low rate (about half of the standard value) it increases up to 83.7 $M_\odot$. These results highlight that carbon burning plays a crucial role in PISNe by determining when a star initiates expansion. The initiation of expansion competes with collapse caused by helium photodisintegration, and the maximum mass that can lead to an explosion depends on the $^{12}\rm{C}\left({\alpha},{\gamma}\right)^{16}\!\rm{O}$ reaction rate.

Authors:Arpan Ghosh, Saurabh Sharma, Joe P. Ninan, Devendra K. Ojha, Bhuwan C. Bhatt, D. K. Sahu, Tapas Baug, R. K. Yadav, Puji Irawati, A. S. Gour, Neelam Panwar, Rakesh Pandey, Tirthendu Sinha, Aayushi Verma

Abstract: We present here the results of eight years of our near-simultaneous optical/near-infrared spectro-photometric monitoring of bonafide FUor candidate `V2493 Cyg' starting from 2013 September to 2021 June. During our optical monitoring period (between October 16, 2015 and December 30, 2019), the V2493 Cyg is slowly dimming with an average dimming rate of $\sim$26.6 $\pm$ 5.6 mmag/yr in V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing towards a gradual expansion of the emitting region post the second outburst. The mid infra-red colors, on the contrary, exhibits a blueing trend which can be attributed to the brightening of the disc due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the H$\alpha$ line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infra-red triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilised compared to the early days of the outburst. The evolution of the O I $\lambda$7773 \AA~ line also points towards the stabilization of the circumstellar disc post the second outburst.

Authors:Emily K Pass, Jennifer G Winters, David Charbonneau, Jonathan M Irwin, Amber A Medina

Abstract: We present results from the volume-complete spectroscopic survey of 0.1-0.3M$_\odot$ M dwarfs within 15pc. This work discusses the active sample without close binary companions, providing a comprehensive picture of these 123 stars with H${\alpha}$ emission stronger than -1$\unicode{xC5}$. Our analysis includes rotation periods (including 31 new measurements), H${\alpha}$ equivalent widths, rotational broadening, inclinations, and radial velocities, determined using high-resolution, multi-epoch spectroscopic data from the TRES and CHIRON spectrographs supplemented by photometry from TESS and MEarth. Using this volume-complete sample, we establish that the majority of active, low-mass M dwarfs are very rapid rotators: specifically, 74$\pm$4% have rotation periods shorter than 2 days, while 19$\pm$4% have intermediate rotation periods of 2-20 days, and the remaining 8$\pm$3% have periods longer than 20 days. Among the latter group, we identify a population of stars with very high H${\alpha}$ emission, which we suggest is indicative of dramatic spindown as these stars transition from the rapidly to slowly rotating modes. We are unable to determine rotation periods for six stars and suggest that some of the stars without measured rotation periods may be viewed pole-on, as such stars are absent from the distribution of inclinations we measure; this lack notwithstanding, we recover the expected isotropic distribution of spin axes. Our spectroscopic and photometric data sets also allow us to investigate activity-induced radial-velocity variability, which we show can be estimated as the product of rotational broadening and the photometric amplitude of spot modulation.

Authors:Jiale Zhang, Hui Tian, Philippe Zarka, Corentin K. Louis, Hongpeng Lu, Dongyang Gao, Xiaohui Sun, Sijie Yu, Bin Chen, Xin Cheng, Ke Wang

Abstract: Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their sub-structures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We detected many radio bursts in the two days of observations with fine structures in the form of numerous millisecond-scale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability which may be related to stellar flares or interactions with a planetary companion.

Authors:Yuri A. Fadeyev

Abstract: Calculations of stellar evolution at initial abundances of helium $Y=0.28$ and heavier elements $Z=0.014$ were done for stars with masses on the main sequence $1.7M_\odot\le M_\textrm{ZAMS}\le 5.2M_\odot$. Evolutionary sequences corresponding to the AGB stage were used for modelling the pulsation period decrease observed for almost two centuries in the Mira--type variable R Hya. Diminution of the period from $\Pi\approx$ 495 d in the second half of the eighteenth century to $\Pi\approx 380$ d in the 1950s is due stellar radius decrease accompanying dissipation of the radiation--diffusion wave generated by the helium flash. For all the history of its observations R Hya was the fundamental mode pulsator. The best agreement with observations is obtained for eight evolutionary models with initial mass $M_\textrm{ZAMS}=4.8M_\odot$ and the mass loss rate parameter of the Bl\"ocker formula $0.03\le\eta_\mathrm{B}\le 0.07$. Theoretical mass estimates of R Hya are in the range $4.44M_\odot\le M\le 4.63M_\odot$, whereas the mean stellar radius ($421R_\odot\le \bar R \le 445R_\odot$) corresponding to the pulsation period $\Pi\approx 380$ agrees well with measurements of the angular diameter by methods of the optical interferometric imaging.

Authors:J. S. Castellanos Durán, A. Korpi-Lagg, S. K. Solanki

Abstract: In addition to the Evershed flow directed from the umbra towards the outer boundary of the sunspot, under special circumstances, a counter Evershed flow (CEF) in the opposite direction also occurs. We aim to characterize the proper motions and evolution of three CEFs observed by the Solar Optical Telescope onboard the Japanese Hinode spacecraft and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. We use state-of-the-art inversions of the radiative transfer equation of polarized light applied to spectropolarimetric observations of the Fe I line pair around 630 nm. The three CEFs appeared within the penumbra. Two of the CEF structures, as part of their decay process, were found to move radially outwards through the penumbra parallel to the penumbral filaments with speeds, deduced from their proper motions, ranging between 65 and 117 m/s. In these two cases, a new spot appeared in the moat of the main sunspot after the CEFs reached the outer part of the penumbra. Meanwhile, the CEFs moved away from the umbra, and their magnetic field strengths decreased. The expulsion of these two CEFs seems to be related to the normal Evershed flow. The third CEF appeared to be dragged by the rotation of a satellite spot. Chromospheric brightenings were found to be associated with the CEFs, and those CEFs that reached the umbra-penumbra boundary showed enhanced chromospheric activity. The two CEFs, for which line-of-sight velocity maps were available during their formation phase, appear as intrusions into the penumbra. They may be associated with magnetic flux emergence.

Authors:Tishtrya Mehta, Anne-Marie Broomhall, Laura Hayes

Abstract: Quasi-periodic pulsations (QPPs) are frequently observed in solar and stellar flare emission, with recent studies suggesting that an increasing instantaneous period is a common characteristic of QPPs. Determining the prevalence of non-stationarity in QPPs contributes to a better understanding of which mechanisms are responsible in QPP generation. We obtain the rate of period evolution from QPPs in 98 M- and X-class flares from Solar Cycle 24 with average periods between 8-130s and investigate the prevalence of QPP non-stationarity. We also investigate whether the presence of a Coronal Mass Ejection (CME) impacts the period evolution of QPPs. We analyse soft X-ray lightcurves obtained from GOES' X-Ray Sensor (XRS) and assess the dominant periods in the impulsive and decay phases of the flares using the Fast Fourier Transform. We relate the rate of period evolution to flare duration, peak flare energy, and average QPP period. We find evidence of non-stationarity in 81% of the flares assessed, with most QPPs exhibiting a period evolution of less than 10s between the impulsive and decay phases, of which 66% exhibited an apparent period growth and 14% showed an apparent period shrinkage. We find a positive correlation between the absolute magnitude of period evolution and the duration of the flare and no correlation between the period evolution of the QPPs and flare energy or CME presence. Furthermore, we conclude that non-stationarity is common in solar QPPs and must be accounted for in flare analysis.

Authors:Aimee Norton, Rachel Howe, Lisa Upton, Ilya Usoskin

Abstract: We describe the defining observations of the solar cycle that provide constraints for the dynamo processes operating within the Sun. Specifically, we report on the following topics: historical sunspot numbers and revisions; active region (AR) flux ranges and lifetimes; tilt angles; Hale and Joy's law; the impact of rogue ARs on cycle progression; the spatio-temporal emergence of ARs that creates the butterfly diagram; polar fields; large-scale flows including zonal, meridional, and AR in-flows; short-term cycle variability; and helioseismic results including mode parameter changes.

Authors:Georgios Chouliaras, P. Syntelis, V. Archontis

Abstract: We have performed 3-D numerical simulations to investigate the effect of partial ionization on the process of magnetic flux emergence. In our study, we have modified the single-fluid MHD equations to include the presence of neutrals and have performed two basic experiments: one that assumes a fully ionized plasma (FI case) and one that assumes a partially ionized plasma (PI case). We find that the PI case brings less dense plasma to and above the solar surface. Furthermore, we find that partial ionization alters the emerging magnetic field structure, leading to a different shape of the polarities in the emerged bipolar regions compared to the FI case. The amount of emerging flux into the solar atmosphere is larger in the PI case, which has the same initial plasma beta as the FI case, but a larger initial magnetic field strength. The expansion of the field above the photosphere occurs relatively earlier in the PI case, and we confirm that the inclusion of partial ionization reduces cooling due to adiabatic expansion. However, it does not appear to work as a heating mechanism for the atmospheric plasma. The performance of these experiments in three dimensions shows that PI does not prevent the formation of unstable magnetic structures, which erupt into the outer solar atmosphere.

Authors:Nadya Serebriakova, Andrew Tkachenko, Sarah Gebruers, Dominic M. Bowman, Timothy Van Reeth, Laurent Mahy, Siemen Burssens, Luc IJspeert, Hugues Sana, Conny Aerts

Abstract: Modern stellar structure and evolution theory experiences a lack of observational calibrations for the interior physics of intermediate- and high-mass stars. This leads to discrepancies between theoretical predictions and observed phenomena mostly related to angular momentum and element transport. Analyses of large samples of massive stars connecting state-of-the-art spectroscopy to asteroseismology may provide clues on how to improve our understanding of their interior structure. We aim to deliver a sample of O- and B-type stars at metallicity regimes of the Milky Way and the Large Magellanic Cloud (LMC) galaxies with accurate atmospheric parameters from high-resolution spectroscopy, along with a detailed investigation of line-profile broadening, for future asteroseismic studies. After describing the general aims of our two Large Programs, we develop dedicated methodology to fit spectral lines and deduce accurate global stellar parameters from high-resolution multi-epoch UVES and FEROS spectroscopy. We use the best available atmosphere models for three regimes covered by our global sample, given its breadth in terms of mass, effective temperature, and evolutionary stage. Aside from accurate atmospheric parameters and locations in the Hertzsprung-Russell diagram, we deliver detailed analyses of macroturbulent line broadening, including estimation of the radial and tangential components. We find that these two components are difficult to disentangle from spectra with signal-to-noise ratios below 250. Future asteroseismic modelling of the deep interior physics of the most promising stars in our sample will improve the existing dearth of such knowledge for large samples of OB stars, including those of low metallicity in the LMC.

Authors:S. A. Deshmukh, H. -G. Ludwig

Abstract: Binary molecules such as CO, OH, CH, CN, and C$_2$ are often used as abundance indicators in stars. These species are usually assumed to be formed in chemical equilibrium. The time-dependent effects of hydrodynamics can affect the formation and dissociation of these species and may lead to deviations from chemical equilibrium. We aim to model departures from chemical equilibrium in dwarf stellar atmospheres by considering time-dependent chemical kinetics alongside hydrodynamics and radiation transfer. We examine the effects of a decreasing metallicity and an altered C/O ratio on the chemistry when compared to the equilibrium state. We used the radiation-(magneto)hydrodynamics code CO5BOLD, and its own chemical solver to solve for the chemistry of 15 species and 83 reactions. The species were treated as passive tracers and were advected by the velocity field. The steady-state chemistry was also computed to isolate the effects of hydrodynamics. In most of the photospheres in the models we present, the mean deviations are smaller than $0.2$ dex, and they generally appear above $\log{\tau} = -2$. The deviations increase with height because the chemical timescales become longer with decreasing density and temperature. A reduced metallicity similarly results in longer chemical timescales and in a reduction in yield that is proportional to the drop in metallicity; a decrease by a factor $100$ in metallicity loosely corresponds to an increase by factor $100$ in chemical timescales. As both CH and OH are formed along reaction pathways to CO, the C/O ratio means that the more abundant element gives faster timescales to the constituent molecular species. Overall, the carbon enhancement phenomenon seen in very metal-poor stars is not a result of an improper treatment of molecular chemistry for stars up to a metallicity as low as [Fe/H] = $-3.0$.

Authors:Øystein Håvard Færder, Daniel Nóbrega-Siverio, Mats Carlsson

Abstract: Magnetic reconnection is a fundamental mechanism in astrophysics. A common challenge in mimicking this process numerically in particular for the Sun is that the solar electrical resistivity is small compared to the diffusive effects caused by the discrete nature of codes. We aim to study different anomalous resistivity models and their respective effects on simulations related to magnetic reconnection in the Sun. We used the Bifrost code to perform a 2D numerical reconnection experiment in the corona that is driven by converging opposite polarities at the solar surface. This experiment was run with three different commonly used resistivity models: 1) the hyper-diffusion model originally implemented in Bifrost, 2) a resistivity proportional to the current density, and 3) a resistivity proportional to the square of the electron drift velocity. The study was complemented with a 1D experiment of a Harris current sheet with the same resistivity models. The 2D experiment shows that the three resistivity models are capable of producing results in satisfactory agreement with each other in terms of the current sheet length, inflow velocity, and Poynting influx. Even though Petschek-like reconnection occurred with the current density-proportional resistivity while the other two cases mainly followed plasmoid-mediated reconnection, the large-scale evolution of thermodynamical quantities such as temperature and density are quite similar between the three cases. For the 1D experiment, some recalibration of the diffusion parameters is needed to obtain comparable results. Specifically the hyper-diffusion and the drift velocity-dependent resistivity model needed only minor adjustments, while the current density-proportional model needed a rescaling of several orders of magnitude.

Authors:M. Gangi, B. Nisini, C. F. Manara, K. France, S. Antoniucci, K. Biazzo, T. Giannini, G. J. Herczeg, J. M. Alcalá, A. Frasca, K. Maucó, J. Campbell-White, M. Siwak, L. Venuti, P. C. Schneider, Á. Kóspál, A. Caratti o Garatti, E. Fiorellino, E. Rigliaco, R. K. Yadav

Abstract: Observing the spatial distribution and excitation processes of atomic and molecular gas in the inner regions (< 20 au) of young (< 10 Myr) protoplanetary disks helps us to understand the conditions for the formation and evolution of planetary systems. In the framework of the PENELLOPE and ULLYSES projects, we aim to characterize the atomic and molecular component of protoplanetary disks in a sample of 11 Classical T Tauri Stars (CTTs) of the Orion OB1 and $\sigma$-Orionis associations. We analyzed the flux-calibrated optical-forbidden lines and the fluorescent ultraviolet $\rm H_2$ progressions using spectra acquired with ESPRESSO at VLT, UVES at VLT and HST-COS. Line morphologies were characterized through Gaussian decomposition. We then focused on the properties of the narrow low-velocity (FWHM < 40 $km$ $s^{-1}$ and |$v_p$| < 30 $km$ $s^{-1}$) component (NLVC) of the [OI] 630 nm line, compared with the properties of the UV-$\rm H_2$ lines. We found that the [OI]630 NLVC and the UV-$\rm H_2$ lines are strongly correlated in terms of peak velocities, full width at half maximum, and luminosity. The luminosities of the [OI]630 NLVC and UV-$\rm H_2$ correlate with the accretion luminosity with a similar slope, as well as with the luminosity of the CIV 154.8, 155 nm doublet. We discuss such correlations in the framework of the currently suggested excitation processes for the [OI]630 NLVC. Our results can be interpreted in a scenario in which the [OI]630 NLVC and UV-$\rm H_2$ have a common disk origin with a partially overlapped radial extension. We also suggest that the excitation of the [OI] NLVC is mainly induced by stellar FUV continuum photons more than being of thermal origin. This study demonstrates the potential of contemporaneous wide-band high-resolution spectroscopy in linking different tracers of protoplanetary disks.

Authors:Anshu Kumari, Diana E. Morosan, E. K. J. Kilpua, F. Daei

Abstract: Metre wavelength type II solar radio bursts are believed to be the signatures of shock-accelerated electrons in the corona. Studying these bursts can give information about the initial kinematics, dynamics and energetics of CMEs in the absence of white-light observations. In this study, we investigate the occurrence of type II bursts in solar cycles 23 and 24 and their association with coronal mass ejections (CMEs). We also explore the possibility of occurrence of type II bursts in the absence of a CME. We performed statistical analysis of type II bursts that occurred between 200 - 25 MHz in solar cycle 23 and 24 and found the temporal association of these radio bursts with CMEs. We categorised the CMEs based on their linear speed and angular width, and studied the distribution of type II bursts with `fast' ($speed ~\geq 500 km/s$), `slow' ($speed ~< 500 km/s$), `wide' ($width ~\geq 60^o$) and `narrow' ($width ~< 60^o$) CMEs. We explored the type II bursts occurrence dependency with solar cycle phases. Our results suggest that type II bursts dominate at heights $\approx 1.7 - 2.3 \pm 0.3 ~R_{\odot}$ with a clear majority having an onset height around 1.7 $\pm 0.3~R_{\odot}$ assuming the four-fold Newkirk model. The results indicate that most of the type II bursts had a white-light CME counterpart, however there were a few type II which did not have a clear CME association. There were more CMEs in cycle 24 than cycle 24. However, the number of type II radio bursts were less in cycle 24 compared to cycle 23. The onset heights of type IIs and their association with wide CMEs reported in this study indicate that the early CME lateral expansion may play a key role in the generation of these radio bursts.

Authors:Belinda Damian, Jessy Jose, Beth Biller, KT Paul

Abstract: Understanding the evolution and dissipation of protoplanetary disks are crucial in star and planet formation studies. We report the protoplanetary disk population in the nearby young $\sigma$ Orionis cluster (d$\sim$408 pc; age$\sim$1.8 Myr) and analyse the disk properties such as dependence on stellar mass and disk evolution. We utilise the comprehensive census of 170 spectroscopic members of the region refined using astrometry from Gaia DR3 for a wide mass range of $\sim$19-0.004 M$_\odot$. Using the near infrared (2MASS) and mid infrared (WISE) photometry we classify the sources based on the spectral index into class I, class II, flat spectrum and class III young stellar objects. The frequency of sources hosting a disk with stellar mass $<$2 M$_\odot$ in this region is 41$\pm$7% which is consistent with the disk fraction estimated in previous studies. We see that there is no significant dependence of disk fraction on stellar mass among T Tauri stars ($<$2 M$_\odot$), but we propose rapid disk depletion around higher mass stars ($>$2 M$_\odot$). Furthermore we find the lowest mass of a disk bearing object to be $\sim$ 20 M$_\mathrm{Jup}$ and the pronounced disk fraction among the brown dwarf population hints at the formation scenario that brown dwarfs form similar to low-mass stars.

Authors:Richard S. Bogart, Charles S. Baldner, Sarbani Basu, Rachel Howe, Maria Cristina Rabello Soares

Abstract: We present evidence of hitherto undiscovered global-scale oscillations in the near-surface shear layer of the Sun. These oscillations are seen as large scale variations of radial shear in both the zonal and meridional flows relative to their mean values. The variations cover all or most of a visible hemisphere, and reverse with a timescale on the order of a solar rotation. A large annual variation in the meridional shear anomaly is understandable in terms of the tilt of the rotation axis, but the rapid oscillations of the shear anomalies in both zonal and the meridional directions appear to be modulated in a more complex, not-quite annual way, although the latter are also strongly modulated by the projected rotational axis angle. Small-scale anomalies in the neighborhood of active regions lend support to their solar origin and physical interpretation. These results were obtained by analyzing ring-diagram fits of low-order modes in high-resolution Doppler data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory.

Authors:Paul Charbonneau, Dmitry Sokoloff

Abstract: In this paper, written as a general historical and technical introduction to the various review papers collected in the special issue ``Solar and Stellar Dynamo: A New Era'', we review the evolution and current state of dynamo theory and modelling, with emphasis on the solar dynamo. Starting with a historical survey, we then focus on a set of ``tension points'' that are still left unresolved despite the remarkable progress of the past century. In our discussion of these tension points we touch upon the physical well-posedness of mean-field electrodynamics; constraints imposed by magnetic helicity conservation; the troublesome role of differential rotation; meridional flows and flux transpost dynamos; competing inductive mechanisms and Babcock-Leighton dynamos; the ambiguous precursor properties of the solar dipole; cycle amplitude regulation and fluctuation through nonlinear backreaction and stochastic forcing, including Grand Minima; and the promises and puzzles offered by global magnethydrodynamical numerical simulations of convection and dynamo action. We close by considering the potential bridges to be constructed between solar dynamo theory and modelling, and observations of magnetic activity in late-type stars.

Authors:Qian-Sheng Zhang, Li Yan, Wu Tao, Jiang Chen

Abstract: In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass SPB star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations and a quick decrease with 4 magnitude orders shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals.

Authors:Hannah E. Brinkman Konkoly Observatory, Research Centre for Astronomy and Earth Sciences Graduate School of Physics, University of Szeged, Hungary Institute of Astronomy, KU Leuven, Leuven, Belgium, C. L. Doherty School of Physics and Astronomy, Monash University, Australia, M. Pignatari Konkoly Observatory, Research Centre for Astronomy and Earth Sciences E. A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, United Kingdom NuGrid Collaboration, O. R. Pols {Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The Netherlands, M. Lugaro Konkoly Observatory, Research Centre for Astronomy and Earth Sciences School of Physics and Astronomy, Monash University, Australia ELTE Eötvös Loránd University, Institute of Physics, Budapest, Hungary

Abstract: Many of the short-lived radioactive nuclei that were present in the early Solar System can be produced in massive stars. In the first paper in this series (Brinkman et al. 2019), we focused on the production of $^{26}$Al in massive binaries. In our second paper (Brinkman et al. 2021), we considered rotating single stars, two more short-lived radioactive nuclei, $^{36}$Cl and $^{41}$Ca, and the comparison to the early Solar System data. In this work, we update our previous conclusions by further considering the impact of binary interactions. We used the MESA stellar evolution code with an extended nuclear network to compute massive (10-80 M$ _{\odot} $), binary stars at various initial periods and solar metallicity (Z=0.014), up to the onset of core collapse. The early Solar System abundances of $^{26}$Al and $^{41}$Ca can be matched self-consistently by models with initial masses $\geq$25 M$_{\odot}$, while models with initial primary masses $\geq$35 M$_{\odot}$ can also match $^{36}$Cl. Almost none of the models provide positive net yields for $^{19}$F, while for $^{22}$Ne the net yields are positive from 30 M$_{\odot}$ and higher. This leads to an increase by a factor of approximately 4 in the amount of $^{22}$Ne produced by a stellar population of binary stars, relative to single stars. Also, besides the impact on the stellar yields, our 10 M$_{\odot}$ primary star undergoing Case A mass-transfer ends its life as a white dwarf instead of as a core-collapse supernova. This demonstrates that binary interactions can also strongly impact the evolution of stars close to the supernova boundary.

Authors:Petri J. Käpylä, Matthew K. Browning, Allan Sacha Brun, Gustavo Guerrero, Jörn Warnecke

Abstract: We review the state of the art of three dimensional numerical simulations of solar and stellar dynamos. We summarize fundamental constraints of numerical modelling and the techniques to alleviate these restrictions. Brief summary of the relevant observations that the simulations seek to capture is given. We survey the current progress of simulations of solar convection and the resulting large-scale dynamo. We continue to studies that model the Sun at different ages and to studies of stars of different masses and evolutionary stages. Both simulations and observations indicate that rotation, measured by the Rossby number which is the ratio of rotation period and convective turnover time, is a key ingredient in setting the overall level and characteristics of magnetic activity. Finally, efforts to understand global 3D simulations in terms of mean-field dynamo theory are discussed.

Authors:D. Gruner, S. A. Barnes, J. Weingrill

Abstract: Gyrochronology allows the derivation of ages for cool main sequence stars from their observed rotation periods and masses, or a suitable proxy of the latter. It is increasingly well explored for FGK stars, but requires further measurements for older ages and K-M-type stars. Recent work has shown that the behavior of stellar spindown differs significantly from prior expectations for late-type stars. We study the 4Gyr-old benchmark open cluster M67 to explore this behavior further. We combined a Gaia DR3 sample with the Kepler K2 superstamp of Campaign 5 around M67 and created new light curves from aperture photometry. The light curves are subjected to an extensive correction process to remove instrumental systematics and trending, followed by period analysis to measure stellar rotation. We identify periodic signals in 136 light curves, 47 of which are from the rotation of effectively single main-sequence stars that span from early-G to mid-M type. These results connect well to prior work on M67 and extend it to much later spectral types. We find that the rotation periods of single stars of age 4Gyr define a tight relationship with color, ranging from spectral types F through M. The corresponding surface of rotation period against age and mass is therefore well-defined to an older age than was previously known. However, the deviations from prior expectations of the stellar spindown behavior are even more pronounced at 4Gyr. The binary cluster members do not follow the single star relationship. The majority are widely scattered below the single star sequence. Consequently, they do not seem to be suitable for gyrochronology at present.