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 t o core collapse. Significant mixing beyond convective boundaries deter mined by mixing-length theory brings fuel (C-12) into the convective r egion, causing hot spots of nuclear burning. Plumes dominate the veloc ity structure. Finite perturbations arise in a region in which O-16 wi ll be explosively burned to Ni-56 when the star explodes; the resultin g instabilities and mixing are likely to distribute Ni-56 throughout t he supernova envelope. Inhomogeneities in Y(e) may be large enough to affect core collapse and will affect explosive nucleosynthesis. The na ture of convective burning is dramatically different from that assumed in one-dimensional simulations; quantitative estimates of nucleosynth etic yields, core masses, and the approach to core collapse will be af fected.