  Using 2D and 3D simulation, we study the "robustness" of the double
detonation scenario for Type Ia supernovae, in which a detonation in the helium
shell of a carbon-oxygen white dwarf induces a secondary detonation in the
underlying core. We find that a helium detonation cannot easily descend into
the core unless it commences (artificially) well above the hottest layer
calculated for the helium shell in current presupernova models. Compressional
waves induced by the sliding helium detonation, however, robustly generate hot
spots which trigger a detonation in the core. Our simulations show that this is
true even for non-axisymmetric initial conditions. If the helium is ignited at
multiple points, the internal waves can pass through one another or be
reflected, but this added complexity does not defeat the generation of the hot
spot. The ignition of very low-mass helium shells depends on whether a
thermonuclear runaway can simultaneously commence in a sufficiently large
region.

High Energy Astrophysical Phenomena;Solar and Stellar Astrophysics