Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs

作者：Fink M^*; Hillebrandt W; Roepke F K

来源：Astronomy & Astrophysics, 2007, 476(3): 1133-1143.

DOI：10.1051/0004-6361:20078438

• supernovae : general
• nuclear reactions, nucleosynthesis, abundances
• hydrodynamics
• methods : numerical

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(circle dot) 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 for He-shell masses of 0.2 and 0.1 M(circle dot) (and thus 0.8 and 0.9 M(circle dot) of C + O), we find that a secondary detonation ignition is a very robust process. Converging shock waves originating from the detonation in the He shell generate the conditions for a detonation near the center of the white dwarf in most of the cases considered. Finally, we follow the complete evolution of three selected models with 0.2 M(circle dot) of He through the C/O-detonation phase and obtain (56)Ni-masses of about 0.40 to 0.45 M(circle dot). Although we have not done a complete scan of the possible parameter space, our results show that sub-Chandrasekhar models are not good candidates for normal or sub-luminous type Ia supernovae. The chemical composition of the ejecta features significant amounts of (56)Ni in the outer layers at high expansion velocities, which is inconsistent with near-maximum spectra.

• 出版日期2007-12