Ignition of detonation in accreted helium

TL;DR

This paper presents the first fully consistent 2D hydrodynamical simulations of helium detonation ignition in accreting white dwarfs, demonstrating that convection can naturally trigger detonations without artificial initiation.

Contribution

It introduces two independent 2D hydrodynamical models that successfully simulate natural helium detonation ignition in accreted envelopes, overcoming previous limitations of artificial ignition methods.

Findings

Detonation can be ignited in a convective cell naturally.

Results are consistent across two different numerical schemes.

Convection plays a crucial role in ignition process.

Abstract

Sub-Chandrasekhar CO white dwarfs accreting helium have been considered as candidates for Type Ia supernova(SNIa) progenitors since the early 1980s (helium shell mass $> 0.1 M_\odot $). These models, once detonated did not fit the observed spectra and light curve of typical SNIa observations. New theoretical work examined detonations on much less massive ($< 0.05 M_\odot $) envelopes. They find stable detonations that lead to light curves, spectra and abundances that compare relatively well with the observational data. The exact mechanism leading to the ignition of helium detonation is a key issue, since it is a mandatory first step for the whole scenario. As the flow of the accreted envelope is unstable to convection long before any hydrodynamic phenomena develops, a multidimensional approach is needed in order to study the ignition process. The complex convective reactive flow is challenging to any hydrodynamical solver. To the best of our knowledge, all previous 2D studies ignited the detonation artificially. We present here, for the first time, fully consistent results from two hydrodynamical 2D solvers that adopt two independent accurate schemes. For both solvers an effort was made to overcome the problematics raised by the finite resolution and numerical diffusion by the advective terms. Our best models lead to the ignition of a detonation in a convective cell. Our results are robust and the agreement between the two different numerical approaches is very good.