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

Abstract

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 perform stellar evolution calculations for the surviving companions of close WD+MS systems in the spin-up/spin-down model and the canonical non-rotating model. This enables us 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 carry out a series of binary population synthesis calculations to obtain the Galactic birth rate of hot subdwarfs from the WD+MS channel, which is $2.3{-}6\times 10^{\rm -4}\, {\rm yr}^{\rm -1}$ for the spin-up/spin-down model and $0.7{-}3\times 10^{\rm -4}\, {\rm yr}^{\rm -1}$ for the canonical non-rotating model. We also show the distributions of some integral properties of the hot subdwarfs, for example the mass and space velocity, for different models. In addition, by comparing our results with observations of intermediate helium-rich (iHe-rich) hot subdwarfs, we find that the hot subdwarfs from the WD+MS channel may explain some observational features of the iHe-rich hot subdwarfs, especially those from the spin-up/spin-down model. Although we expect that the SN Ia channel will contribute only a small fraction of the iHe-rich hot subdwarf population, some of these may help to explain cases with unusual kinematics.