He-accreting oxygen-neon white dwarfs and accretion-induced collapse events

TL;DR

This study uses MESA simulations to explore how helium accretion on oxygen-neon white dwarfs affects their composition and the likelihood of collapsing into neutron stars, providing insights into accretion-induced collapse events.

Contribution

It is the first detailed investigation of elemental abundance changes on He-accreting ONe WDs approaching Mch, highlighting the formation of Si and the collapse process.

Findings

A CO-rich mantle forms beneath He layers after He burning.

The amount of Si produced is inversely related to accretion rate.

Most ONe WDs near Mch are likely to undergo accretion-induced collapse.

Abstract

It has been widely accepted that mass-accreting white dwarfs (WDs) are the progenitors of Type Ia supernovae or electron-capture supernovae. Previous work has shown that the accretion rate could affect the elemental abundance on the outer layers of CO WDs, and therefore affect the observational characteristics after they exploded as SNe Ia. However, it has not been well studied how elemental abundance changes on the outer layers of He-accreting ONe WDs as they approach the Chandrasekhar mass limit. In this paper, we investigated the evolution of He-accreting ONe WDs with MESA. We found that a CO-rich mantle will accumulate beneath the He layers resulting from the He burning, after which the ignition of the CO-rich mantle could transform carbon into silicon (Si). The amount of Si produced by carbon burning is strongly anti-correlated with the accretion rate. As the ONe WD nearly approaches the Chandrasekhar mass limit (Mch) through accretion, it is likely to undergo accretion-induced collapse (AIC), resulting in the formation of the neutron star (NS).