The fates of binary companions in Type Ia supernovae within the single-degenerate scenario

Binaries;Numerical;Stars:evolution;Supernovae;Hydrodynamics

Pan, Kuo-Chuan

关键词: Binaries;    Numerical;    Stars:evolution;    Supernovae;    Hydrodynamics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45421/Kuo-Chuan_Pan.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Type Ia supernovae (SNe~Ia) are thought to be caused by thermonuclear explosions of carbon-oxygenwhite dwarfs in close binary systems. However, the nature of the progenitor systems isstill uncertain. In the single-degenerate scenario (SDS), the companion star is non-degenerateand can be significantly affected by the explosion.We explore this interaction by means ofmulti-dimensional adaptive mesh refinement simulations using the FLASH code.We consider several different companion types, including main-sequence-like stars, red giants,and helium stars. In addition, we include the symmetry-breaking effects of orbital motion,rotation of the non-degenerate star, and Roche-lobe overflow.We find that the relationship between the unbound stellar mass and the initial binary separation can befitted by a power law. The power-law index is found to be about $-3.5$ to $-3.7$for the main-sequence star, $-2.9$ to $-3.4$ for the helium star,and $-4.0$ to $-4.2$ for the red giant.After the explosion, the companion receives a kick from the supernova ejecta.It is found that the kick velocity is also related to the binary separation by a power law,except for the red giant companion, due to the large numerical uncertainty created by the small kickin this case. The power-law index is found to be about $-1.7$ to $-1.9$ for the main-sequence starand $-2.6$ to $-2.8$ for the helium star.By using tracer particles in FLASH, the process leading to the unbinding of matter can be determinedby analyzing the fluid elements in a time sequence.It is found that the process is dominated by ablation, which has usually been neglected inpast analytical studies.The level of Ni/Fe contamination of the companion that results from the passage of the supernova ejectais found to be$\sim 10^{-5} M_\odot$ for the main-sequence star,$\sim 10^{-4} M_\odot$ for the He star, and$\sim 10^{-8} M_\odot$ for the red giant,suggesting that the ratio of nickel/iron to hydrogen plus helium abundance in the remnantshould be found to be larger than the solar ratio if the contamination is mixed only in thecompanion's envelope.A hole in the ejecta shadowed by the companion star is also found in the simulation,which is a possible source of the variation in SN~Ia light curves.The spinning main-sequence companion star loses about $48\%$ of its initial angular momentumduring the impact,causing the rotational velocity to drop to $23\%$ of the original rotational velocity.One way to distinguish between the single- and double-degenerate scenarios is to search forthe post-impact remnant star expected in the SDS. We explore the evolution of the post-impactremnants in our simulations for main sequence-like and helium-rich star binary companions using thestellar evolution code MESA.Our results show that the energy deposited in a main sequence companion'souter layers by the SN causes the outermost $\sim 5$\% of the star toexpand on the local thermal timescale ($\sim 300-1000$~yr), making thestar brighten to $\sim 10-100L_\odot$. In most cases the effective temperaturealso increases significantly. As this excess energy is radiated away, theouter layers slowly recollapse. The time evolution is sensitive not only tothe amount of SN energy deposited but also the depth to which it penetrates.For Tycho G, the proposed remnant of Tycho's SN, we find that main sequencecompanions can match the observed effective temperature and rotation speed(assuming conservation of specific angular momentum post-impact), but theyare typically $\sim 2\times$ too bright.We have also examined helium star models for both normal SNe~Ia andthe newly classified subluminous ``Type Iax'' SNeand find that these cases follow very different Hertzsprung-Russell (H-R)diagram tracks than do main sequence models. Heliumstar companions brighten to $\sim 10^4 L_\odot$ within a decade, becominghot blue subdwarfs (sdOs) and contracting over $> 10^6$~yr to become heliumred giants.Because helium star companions start in more compact systems,their kick velocities and rotation speeds can be much higher than for mainsequence companions.Our results show that, given the age of a supernova remnant, we can test the plausibilityof candidate observed remnant companions, and based on such comparisons wecan draw conclusions about the nature of the companions, if the SDS is valid.Moreover, the luminosity enhancements due to SN impact can be sufficient to make remnantcompanion stars detectable in the Magellanic Clouds or other nearby galaxies with distances$\lesssim 4$~Mpc.