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

Employing Eggleton’s stellar evolution code with the 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 ～0.3×10^?3 yr^?1, and that this channel can produce SNe Ia with short delay times (～45–140 Myr). We also find that the surviving companion stars in this channel have a high spatial velocity (>400 km/s) after the SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.