THE DELAYED-DETONATION MODEL OF TYPE-IA SUPERNOVAE .2. THE DETONATIONPHASE

The investigation, by use of two-dimensional numerical hydrodynamics s imulations, of the ''delayed detonation'' mechanism of Khokhlov for th e explosion of Type Ia supernovae is continued. Previously we found th at the deflagration is insufficient to unbind the star. Expansion shut s off the flame; much of this small production of iron group nuclei oc curs at lower densities, which reduces the electron-capture problem. B ecause the degenerate star has an adiabatic exponent only slightly abo ve 4/3, the energy released by deflagration drives a pulsation of larg e amplitude. During the first expansion phase, adiabatic cooling shuts off the burning, and a Rayleigh-Taylor instability then gives mixing of high-entropy ashes with low-entropy fuel. During the first contract ion phase, compressional heating reignites the material. The burning w as allowed to develop into a detonation in these nonspherical models. The detonation grows toward spherical symmetry at late times. At these densities (rho approximately 10(7) to 10(8) g cm-3), either Ni-56 or nuclei of the Si-Ca group are the dominant products of the burning. Th e bulk yields are sensitive to the density of the star when the transi tion to detonation occurs. The relevance of the abundances, velocities , mixing, and total energy release to the theory and interpretation of Type la supernovae is discussed.