Cellular Dynamics of Helium-rich Detonation on Sub-Chandrasekhar Mass White Dwarf

Abstract In previous hydrodynamic studies on detonation in the context of Type Ia supernovae (SNe Ia), consideration of cellular structures has been limited in the evaluation of a criterion in initiation, propagation, quenching, and the resolution requirement of detonation, whereas it is quite common to consider cell sizes in the discussion on terrestrial detonation in chemically reactive systems. In our recent study, the terrestrial cell-based theories, which incorporate the cell-size data acquired in two-dimensional simulations of helium detonation in the double-detonation model, were demonstrated to be powerful diagnostics in reproducing the thresholds in the initiation and quenching provided by previous studies. In the present study, two-dimensional simulation results of the cellular detonation in the base of a white dwarf's (WD) envelope are described in detail, in terms of the dynamic wave morphology and chemical abundance structure. The cellular structure is observed at a range of upstream density and envelope composition explored in the present work. C/O contamination by the WD's core material reduces the cell width rapidly, as accelerated by the α -capture reaction. It is also indicated that nickel production could be significantly delayed for the C/O-rich composition. The small cell width requires the detonation structure to be resolved in full-star simulations of SNe Ia, which could raise concerns about the robustness of the outcomes of some numerical simulations in terms of the success and failure of detonation. This issue may be overcome by subgrid modeling that incorporates the cellular dynamics acquired in resolved simulations.