Accreting White Dwarfs: Effect of WD Composition on Helium Ignition During Slow Accretion

TL;DR

This study investigates how the composition of white dwarfs influences helium ignition during slow accretion, using simulations to analyze changes in stellar properties and ignition timing.

Contribution

It provides new insights into the impact of WD composition, especially carbon abundance, on helium ignition delay during accretion, using detailed stellar simulations.

Findings

Lower carbon abundance leads to longer accretion phases before ignition.

Specific heat and degeneracy parameter profiles show distinct features near ignition.

White dwarf size decreases and gravity increases during accretion.

Abstract

Understanding the explosion mechanism of type Ia supernova is among the most challenging issues in astrophysics. Accretion of matter on a carbon-oxygen white dwarf from a companion star is one of the most important keys in this regard. Our aim is to study the effects of WD composition on various parameters during the accretion of helium rich matter at a slow rate. We have used the computer simulation code Modules for Experiments in Stellar Astrophysics (MESA) to understand the variations in the properties such as specific heat (\textit{$C_P$}) and degeneracy parameter (\textit{$\eta$}). The profile of specific heat shows a discontinuity and that of the degeneracy parameter shows a dip near the ignition region. As expected, the size of WD decreases and \textit{g} increases during the accretion. However, a red-giant-like expansion is observed after the rapid ignition towards the end. Our study explains the reason behind the delay in onset of helium ignition due to the difference in carbon abundance in a CO-WD. We find that white dwarfs of the lower abundance of carbon accrete slightly longer before the onset of helium ignition.