Solar and Stellar Astrophysics (astro-ph.SR)

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.

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.