THE QUASI-STATIC EVOLUTION OF ONEMG CORES - EXPLOSIVE IGNITION DENSITIES AND THE COLLAPSE EXPLOSION ALTERNATIVE

The quasi-static evolution of an electron-degenerate ONeMg core is followed up to the point of explosive Ne-O ignition triggered by electron capture. Recently calculated electron-capture rates on Mg-24, Na-24, Ne-20, and F-20 are used, and the ignition density is found to be rho(ign) congruent-to 8.5 x 10(9) g cm-3 (when the Ledoux criterion for convection is adopted), instead of rho(ign) congruent-to 10(10) g cm-3 as in earlier calculations. Such a comparatively low ignition density should lead to complete explosive disruption of the core even if the thermonuclear burning propagated all the way as a conductive, laminar flame. The dependence of the ignition density on the treatment adopted for mixing in the semiconvective region and the astronomical implications of our results are briefly discussed.