Helium star evolutionary channel to super-Chandrasekhar mass type Ia supernovae

TL;DR

This study models the evolution of helium star and white dwarf binaries to explore how super-Chandrasekhar mass white dwarfs can lead to overluminous type Ia supernovae, highlighting the conditions and mass limits involved.

Contribution

It introduces a numerical simulation of binary systems with helium stars and white dwarfs to identify parameters leading to super-Chandrasekhar mass supernovae, expanding understanding of their progenitors.

Findings

Super-Chandrasekhar mass WDs up to 1.81 M_sun can form from 1.2 M_sun initial WDs.

Massive WDs (>1.85 M_sun) cannot be formed in these systems.

Explosive masses for 1.0 M_sun initial WDs are nearly uniform, explaining their observational rarity.

Abstract

Recent discovery of several overluminous type Ia supernovae (SNe Ia) indicates that the explosive masses of white dwarfs may significantly exceed the canonical Chandrasekhar mass limit. Rapid differential rotation may support these massive white dwarfs. Based on the single-degenerate scenario, and assuming that the white dwarfs would differentially rotate when the accretion rate $\dot{M}>3\times 10^{-7}M_{\odot}\rm yr^{-1}$, employing Eggleton's stellar evolution code we have performed the numerical calculations for $\sim$ 1000 binary systems consisting of a He star and a CO white dwarf (WD). We present the initial parameters in the orbital period - helium star mass plane (for WD masses of $1.0 M_{\odot}$ and $1.2 M_{\odot}$, respectively), which lead to super-Chandrasekhar mass SNe Ia. Our results indicate that, for an initial massive WD of $1.2 M_{\odot}$, a large number of SNe Ia may result from super-Chandrasekhar mass WDs, and the highest mass of the WD at the moment of SNe Ia explosion is 1.81 $M_\odot$, but very massive ($>1.85M_{\odot}$) WDs cannot be formed. However, when the initial mass of WDs is $1.0 M_{\odot}$, the explosive masses of SNe Ia are nearly uniform, which is consistent with the rareness of super-Chandrasekhar mass SNe Ia in observations.