The progenitors of Type Ia supernovae with long delay times

TL;DR

This study investigates the progenitors of Type Ia supernovae with long delay times by modeling binary evolution, revealing the conditions under which white dwarf binaries can produce SNe Ia and estimating their birthrates.

Contribution

It provides new initial parameter mappings for WD binaries leading to SNe Ia and estimates their Galactic birthrates, highlighting the significance of the WD + MS channel.

Findings

WD + MS channel can produce SNe Ia with low-mass WDs (~0.61 M_)

Galactic SN Ia birthrate from WD + MS channel is  1.8  10^{-3} yr^{-1}

Birthrate from WD + RG channel remains low (~3  10^{-5} yr^{-1})

Abstract

The nature of the progenitors of Type Ia supernovae (SNe Ia) is still unclear. In this paper, by considering the effect of the instability of accretion disk on the evolution of white dwarf (WD) binaries, we performed binary evolution calculations for about 2400 close WD binaries, in which a carbon--oxygen WD accretes material from a main-sequence star or a slightly evolved subgiant star (WD + MS channel), or a red-giant star (WD + RG channel) to increase its mass to the Chandrasekhar (Ch) mass limit. According to these calculations, we mapped out the initial parameters for SNe Ia in the orbital period--secondary mass ($\log P^{\rm i}-M^{\rm i}_2$) plane for various WD masses for these two channels, respectively. We confirm that WDs in the WD + MS channel with a mass as low as $0.61 M_\odot$ can accrete efficiently and reach the Ch limit, while the lowest WD mass for the WD + RG channel is $1.0 \rm M_\odot$. We have implemented these results in a binary population synthesis study to obtain the SN Ia birthrates and the evolution of SN Ia birthrates with time for both a constant star formation rate and a single starburst. We find that the Galactic SN Ia birthrate from the WD + MS channel is $\sim$$1.8\times 10^{-3} {\rm yr}^{-1}$ according to our standard model, which is higher than previous results. However, similar to previous studies, the birthrate from the WD + RG channel is still low ($\sim$$3\times 10^{-5} {\rm yr}^{-1}$). We also find that about one third of SNe Ia from the WD + MS channel and all SNe Ia from the WD + RG channel can contribute to the old populations ($\ga$1 Gyr) of SN Ia progenitors.