The response of a helium white dwarf to an exploding type Ia supernova

TL;DR

This study uses numerical simulations to explore how helium white dwarf donors respond to and influence Type Ia supernova explosions, revealing conditions for helium ignition, shadow effects, and potential observational signatures.

Contribution

It provides new insights into the interaction between exploding CO white dwarfs and helium WD donors, including conditions for helium detonation and implications for supernova observations.

Findings

Low-mass He WD donors do not ignite helium and create ejecta shadows.

More massive He WD donors can detonate helium, leading to triple detonation scenarios.

Approximately 0.15Msun of unburned helium is ejected, possibly observable as a peculiar type Ib supernova.

Abstract

We conduct numerical simulations of the interacting ejecta from an exploding CO white dwarf (WD) with a He WD donor in the double-detonation scenario for Type Ia supernovae (SNe Ia), and study the possibility of exploding the companion WD. We also study the long time imprint of the collision on the supernova remnant. When the donor He WD has a low mass, M_WD = 0.2Msun, it is at a distance of ~ 0.08Rsun from the explosion, and helium is not ignited. The low mass He WD casts an 'ejecta shadow' behind it. By evolving the ejecta for longer times, we find that the outer parts of the shadowed side are fainter and its boundary with the ambient gas is somewhat flat. More massive He WD donors, M_WD ~ 0.4Msun, must be closer to the CO WD to transfer mass. At a distance of a < 0.045Rsun helium is detonated and the He WD explodes, leading to a triple detonation scenario. In the explosion of the donor WD approximately 0.15Msun of unburned helium is ejected. This might be observed as a peculiar type Ib supernova.