Hot subdwarfs from the surviving companions of the white dwarf + main-sequence channel of Type Ia supernovae

TL;DR

This study models the evolution of surviving companions from white dwarf + main-sequence supernova progenitors to hot subdwarfs, estimating their Galactic birth rates and comparing properties with observations of helium-rich hot subdwarfs.

Contribution

It introduces detailed stellar evolution and population synthesis models for hot subdwarfs from the WD + MS supernova channel, including the spin-up/spin-down scenario.

Findings

Galactic birth rate of hot subdwarfs from this channel is estimated.

Distributions of mass and velocity of these hot subdwarfs are provided.

Some observed helium-rich hot subdwarfs may originate from this channel.

Abstract

Some surviving companions of type Ia supernovae (SNe Ia) from the white-dwarf + main-sequence (WD + MS) channel may evolve to hot subdwarfs. In this paper, we preformed stellar evolution calculations for surviving companions of close WD + MS systems in the spin-up/spin-down model and the canonical non-rotating model to map out the initial parameter spaces in the orbital period - secondary mass plane in which the surviving companions can evolve to hot subdwarfs. Based on these results, we carried out a series of binary population synthesis calculation to obtain the Galactic birth rate of the hot subdwarfs from the WD + MS channel, which is $2.3-6\times10^{\rm -4}\,{\rm yr}^{\rm -1}$ for the spin-up/spin-down model and $0.7-3\times10^{\rm -4}\,{\rm yr}^{\rm -1}$ for the canonical non-rotating model. We also show the distributions of some integral properties of the hot subdwarfs, e.g. the mass and the space velocity, for different models. In addition, comparing our results with the observations of the intermediate helium-rich (iHe-rich) hot subdwarfs, the hot subdwarfs from the WD + MS channel may explain some observational features of the iHe-rich hot subdwarfs, especially for those from the spin-up/spin-down model. Although we expect that the SN Ia channel can only contribute a small fraction of the iHe-rich hot subdwarf population, some of these may help to explain cases with unusual kinematics.