2-DIMENSIONAL HYDRODYNAMICS OF PRECORE COLLAPSE - OXYGEN SHELL BURNING

By direct hydrodynamic simulation, using the piecewise parabolic metho d code PROMETHEUS, we study the properties of a convective oxygen-burn ing shell in a SN 1987A progenitor star (20 M-.) prior to collapse. Th e convection is too heterogeneous and dynamic to be well approximated by one-dimensional diffusion-like algorithms that have previously been used for this epoch. Qualitatively new phenomena are seen. The simula tions are two-dimensional, with good resolution in radius and angle, a nd used a large (90 degrees) slice centered at the equator. The microp hysics and the initial model were carefully treated. Many of the quali tative features of previous multidimensional simulations of convection are seen, including large kinetic and acoustic energy fluxes, which a re not accounted for by mixing length theory. Small but significant am ounts of C-12 are mixed nonuniformly into the oxygen-burning convectio n zone, resulting in hot spots of nuclear energy production that are m ore than an order of magnitude more energetic than the oxygen flame it self, Density perturbations (up to 8%) occur at the ''edges'' of the c onvective zone and are the result of gravity waves generated by intera ction of penetrating flows into the stable region. Perturbations of te mperature and Y-e(or neutron excess eta) at the base of the convective zone are of sufficient magnitude to create angular inhomogeneities in explosive nucleosynthesis products and need to be included in quantit ative estimates of yields. Combined with the plumelike velocity struct ure arising from convection, the perturbations will contribute to the mixing of Ni-56 throughout supernovae envelopes. Runs of different res olution and angular extent were performed to test the robustness of th ese simulations.