On the rotation properties of a post-explosion helium-star companion in Type Iax supernovae

TL;DR

This study models the post-explosion rotation of helium-star companions in Type Iax supernovae, revealing they spin down significantly after impact and then spin up again, which could aid in identifying such survivors.

Contribution

It extends previous hydrodynamical simulations by including orbital and spin velocities, and tracks the post-impact rotational evolution of helium-star companions using stellar evolution modeling.

Findings

He-star companions spin down to one-third of their original rotation after impact.

The star's surface rotational speed varies significantly during post-impact evolution.

The spin-switching behavior may help identify surviving companions in observations.

Abstract

Recent studies have suggested that type Iax supernovae (SNe Iax) are likely to result from a weak deflagration explosion of a Chandrasekhar-mass white dwarf in a binary system with a helium (He)-star companion. Assuming that most SNe Iax are produced from this scenario, in this work we extend our previous work on the three-dimensional hydrodynamical simulation of ejecta-companion interaction by taking the orbital and spin velocities of the progenitor system into account. We then follow the post-impact evolution of a surviving He-star companion by using the one-dimensional stellar evolution code \textsc{MESA}. We aim to investigate the post-explosion rotation properties of a He-star companion in SNe Iax. We find that the He-star companion spins down after the impact due to the angular-momentum loss and expansion caused by the mass-stripping and shock heating during the interaction. This leads to the situation where the surface rotational speed of the surviving companion can drop to one-third of its pre-explosion value when it expands to a maximum radius a few years after the impact. Subsequently, the star shrinks and spins up again once the deposited energy is released. This spin-switching feature of the surviving He-star companions of SNe Iax may be useful for the identification of such objects in future observations.