Thermonuclear detonations ensuing white dwarf mergers

TL;DR

This study investigates white dwarf mergers as progenitors of type Ia supernovae, analyzing ignition, detonation, and nucleosynthesis across various mass and composition configurations, identifying models consistent with observed supernovae.

Contribution

It provides the first comprehensive analysis of detonation initiation and nucleosynthesis in diverse white dwarf merger scenarios, linking specific configurations to observed supernova types.

Findings

Three models match all observational constraints.

One model produces a sub-luminous SN 1991bg-like event.

Two models are potential standard SNe Ia candidates.

Abstract

The merger of two white dwarfs (WDs) has for many years not been considered as the favoured model for the progenitor system of type Ia supernovae (SNe Ia). But recent years have seen a change of opinion as a number of studies, both observational and theoretical, have concluded that they should contribute significantly to the observed type Ia supernova rate. In this paper, we study the ignition and propagation of detonation through post-merger remnants and we follow the resulting nucleosynthesis up to the point where a homologous expansion is reached. In our study we cover the entire range of WD masses and compositions. For the emergence of a detonation we study three different setups. The first two are guided by the merger remnants from our earlier simulations (Dan et al. 2014}, while for the third one the ignitions were set by placing hotspots with properties determined by spatially resolved calculations taken from the literature. There are some caveats to our approach which we investigate. We carefully compare the nucleosynthetic yields of successful explosions with SN Ia observations. Only three of our models are consistent with all the imposed constraints and potentially lead to a standard type Ia event. The first one, a $0.45\,M_\odot\ {\rm helium\ (He)} + 0.9 \,M_\odot$ carbon-oxygen (CO) WD system produces a sub-luminous, SN 1991bg-like event while the other two, a $0.45\,M_\odot\ {\rm He} + 1.1\,M_\odot$ oxygen-neon (ONe) WD system and a $1.05+1.05\,M_\odot$ system with two CO WDs, are good candidates for common SNe Ia.