Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs

Abstract

Type Ia supernovae are believed to be white dwarfs disrupted by a thermonuclear explosion. Here we investigate the scenario in which a rather low-mass, carbon-oxygen (C + O) white dwarf accumulates helium on its surface in a sufficient amount for igniting a detonation in the helium shell before the Chandrasekhar mass is reached. In principle, this can happen on white dwarfs accreting from a non-degenerate companion or by merging a C + O white dwarf with a low-mass helium one. In this scenario, the helium detonation is thought to trigger a secondary detonation in the C + O core. It is therefore called the “double-detonation sub-Chandrasekhar” supernova model. By means of a set of numerical simulations, we investigate the robustness of this explosion mechanism for generic 1-M� models and analyze its observable predictions. Also a resolution dependence in numerical simulations is analyzed. Hydrodynamic simulations of the double-detonation sub-Chandrasekhar scenario are conducted in two and three spatial dimensions. The propagation of thermonuclear detonation fronts, both in helium and in the carbon-oxygen mixture, is computed by means of both a level-set function and a simplified description for nuclear reactions. The decision whether a secondary detonation is triggered in the white dwarf’s core or not is made based on criteria given in the literature. In a parameter study involving different initial flame geometries − − − [ � ] ] −