THE DELAYED-DETONATION MODEL OF A TYPE-IA SUPERNOVAE .1. THE DEFLAGRATION PHASE

The nature of the ''delayed detonation'' mechanism of Khokhlov for the explosion of Type Ia supernovae is investigated by using two-dimensio nal numerical hydrodynamics simulations. A new algorithm is used to tr eat the deflagration front. Assuming that it propagates locally at the laminar flame speed, the deflagration is insufficient to unbind the s tar. Expansion shuts off the flame; much of this small production of i ron group nuclei occurs at lower densities, which reduces the electron -capture problem. The burning front does become wrinkled, but the wave length of the instability is much larger than the computational grid s ize and is resolved; this is consistent with previous analysis. Becaus e the degenerate star has an adiabatic exponent only slightly above 4/ 3, the energy released by deflagration drives a pulsation of large amp litude. During the first expansion phase, adiabatic cooling shuts off the burning, and a Rayleigh-Taylor instability then gives mixing of hi gh-entropy ashes with low-entropy fuel. During the first contraction p hase, compressional heating reignites the material. This paper deals w ith the deflagration phase, from the onset of burning, through expansi on and quenching of the flame, to the first contraction.