Convection, nucleosynthesis, and core collapse

We use a piecewise parabolic method hydrodynamics code (PROMETHEUS) to study convective burning in two dimensions in an oxygen shell prior to core collapse. Significant mixing beyond convective boundaries determined by mixing-length theory brings fuel (¹²C) into the convective regon, causing hot spots of nuclear burning. Plumes dominate the velocity structure. Finite perturbations arise in a region in which ¹⁶O will be explosively burned to ⁵⁶Ni when the star explodes; the resulting instabilities and mixing are likely to distribute ⁵⁶Ni throughout the supernova envelope. Inhomogeneities in Y_e may be large enough to affect core collapse and will affect explosive nucleosynthesis. The nature of convective burning is dramatically different from that assumed in one-dimensional simulations; quantitative estimates of nucleosynthetic yields, core masses, and the approach to core collapse will be affected.