Silicon Burning. II. Quasi‐Equilibrium and Explosive Burning

Having examined the application of quasi-equilibrium to hydrostatic siliconburning in Paper I of this series, Hix & Thielemann (1996), we now turn ourattention to explosive silicon burning. Previous authors have shown that formaterial which is heated to high temperature by a passing shock and then cooledby adiabatic expansion, the results can be divided into three broad categories;\emph{incomplete burning}, \emph{normal freezeout} and \emph{$\alpha$-richfreezeout}, with the outcome depending on the temperature, density and coolingtimescale. In all three cases, we find that the important abundances obeyquasi-equilibrium for temperatures greater than approximately 3 GK, withrelatively little nucleosynthesis occurring following the breakdown ofquasi-equilibrium. We will show that quasi-equilibrium provides betterabundance estimates than global nuclear statistical equilibrium, even fornormal freezeout and particularly for $\alpha$-rich freezeout. We will alsoexamine the accuracy with which the final nuclear abundances can be estimatedfrom quasi-equilibrium.Comment: 27 pages, including 15 inline figures. LaTeX 2e with aaspp4 and graphicx packages. Accepted to Ap