Solar and Stellar Astrophysics (astro-ph.SR)

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).

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.

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.

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.

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.