Long-term evolution of post-explosion Helium-star Companions of Type Iax Supernovae

TL;DR

This study models the long-term post-explosion evolution of helium-star companions in Type Iax supernova systems, predicting their observable properties to aid future identification and understanding of their progenitors.

Contribution

It provides the first detailed stellar evolution models of surviving helium companions after SNe Iax explosions, linking explosion impact to observable features.

Findings

Surviving helium companions' luminosity increases significantly post-impact.

They evolve into hot subdwarf (sdO) stars over ~10,000 years.

Predicted properties can help identify surviving companions in observations.

Abstract

Supernovae of Type Iax (SNe Iax) are an accepted faint subclass of hydrogen-free supernovae. Their origin, the nature of the progenitor systems, however, is an open question. Recent studies suggest that the weak deflagration explosion of a near-Chandrasekhar-mass white dwarf in a binary system with a helium star donor could be the origin of SNe Iax. In this scenario, the helium star donor is expected to survive the explosion. We use the one-dimensional stellar evolution codes \textsc{MESA} and \textsc{Kepler} to follow the post-impact evolution of the surviving helium companion stars. The stellar models are based on our previous hydrodynamical simulations of ejecta-donor interaction, and we explore the observational characteristics of these surviving helium companions. We find that the luminosities of the surviving helium companions increase significantly after the impact: They could vary from $2\mathord,500\,\mathrm{L_{\odot}}$ to $16\mathord,000\,\mathrm{L_{\odot}}$ for a Kelvin-Helmholtz timescale of about $10^{4}\,\mathrm{yr}$. After the star reaches thermal equilibrium, it evolves as an O-type hot subdwarf (sdO) star and continues its evolution along the evolutionary track of a normal sdO star with the same mass. Our results will help to identify the surviving helium companions of SNe Iax in future observations and to place new constraints on their progenitor models.