Local two-dimensional simulations of the ignition of a helium shell detonation on a white dwarf by an impacting stream

TL;DR

This study uses 2D simulations to explore how impacting streams can trigger helium shell detonations on white dwarfs, supporting the viability of the D6 double detonation model for Type Ia supernovae.

Contribution

It demonstrates that stream impact can directly cause surface detonations across various parameters, validating the D6 scenario as a plausible explosion mechanism.

Findings

Stream impact can cause surface detonation at lower shell densities.

Thinner helium shells ignite more promptly upon impact.

Lower limits on shell density and stream speed are below previous estimates.

Abstract

The double detonation model is one of the prevalent explosion mechanisms of Type Ia Supernovae (SNe Ia) wherein an outer helium shell detonation triggers a core detonation in the white dwarf (WD). The dynamically driven double degenerate double detonation (D6) is the double detonation of the more massive WD in a binary WD system where the localized impact of the mass transfer stream from the companion sets off the initial helium shell detonation. To have high numerical resolution and control over the stream parameters, we have implemented a study of the local interaction of the stream with the WD surface in 2D. In cases with lower base density of the shell, the stream's impact can cause surface detonation soon after first impact. With higher base densities, after the stream hits the surface, hot material flows around the star and interacts with the incoming stream to produce a denser and narrower impact. Our results therefore show that (1) a directly impacting stream for both a relatively high resolution and for a range of stream parameters can produce a surface detonation, (2) thinner helium shells ignite more promptly via impact, doing so sooner, and (3) there are lower limits on ignition in both shell density and incoming stream speed with lower limits on density being well below those shown by other work to be required for normal appearing SN Ia. This supports stream ignition and therefore the D6 scenario, as a viable mechanism for normal SNe Ia.