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

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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 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 SN explosion, which could be an alternative origin for hypervelocity stars (HVSs), especially for HVSs such as US 708.