OXYGEN-BURNING HYDRODYNAMICS .1. STEADY SHELL BURNING

With new hydrodynamic techniques, the relatively fast evolutionary sta ges of a star prior to core collapse may be explicitly computed in two spatial dimensions, with a treatment of the microphysics (e.g., nucle ar reactions, equation of state, neutrino cooling) which is comparable to typical one-dimensional simulations. The nature of shell oxygen bu rning in a massive star, prior to core collapse, is used as a first ex ample; it is of particular interest because it is (1) the region in wh ich Ni-56 will be produced by the supernova shock, (2) the region of t he ''mass cut,'' which will separate the collapsed core from the eject ed mantle, (3) the site of much of the explosive nucleosynthesis, and (4) a suggested source of symmetry breaking to drive mixing instabilit ies which were observed in SN 1987A. The nature of the shell burning a ffects the size of the core which will collapse. The method is illustr ated on this test case, and the character of the convection is examine d.