WD + He star systems as the progenitors of Type Ia supernovae and their surviving companion stars

TL;DR

This study investigates the WD + He star channel as a pathway for Type Ia supernovae, analyzing progenitor parameters, birthrates, and the properties of surviving companion stars, including their potential link to hypervelocity stars.

Contribution

It provides a systematic analysis of the WD + He star channel using stellar evolution and population synthesis, highlighting its role in producing SNe Ia and hypervelocity stars.

Findings

Galactic SN Ia birthrate from this channel is approximately 0.0003 per year.

This channel can produce SNe Ia with short delay times of 45-140 million years.

Surviving companion stars can have velocities exceeding 400 km/s, possibly explaining hypervelocity stars like US 708.

Abstract

Employing Eggleton's stellar evolution code with an optically thick wind assumption, we have systematically studied the WD + He star channel of Type Ia supernovae (SNe Ia), in which a carbon-oxygen WD accretes material from a He main-sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. We mapped out the parameter spaces for producing SNe Ia. According to a detailed binary population synthesis approach, we find that the Galactic SN Ia birthrate from this channel is $\sim$$0.3\times 10^{-3} {\rm yr}^{-1}$, and that this channel can produce SNe Ia with short delay times ($\sim45-$140 Myr). We also find that the surviving companion stars in this channel have a high spatial velocity ($>$400 km/s) after SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.