Silicon Burning, Quasi-Equilibrium and the formation of the Iron Peak

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Session 79 -- Supernovae: Observations and Theory
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[79.04] Silicon Burning, Quasi-Equilibrium and the formation of the Iron Peak

William Raphael Hix (Center for Astrophysics), Friedrich-Karl Thielemann (University of Basel)

As the most tightly bound nuclei, the 'Iron Peak' nuclei result from Nuclear Statistical Equilibrium (NSE) and are the culmination of nuclear energy generation in astrophysical environments. Our re-examination of silicon burning, the mechanism by which the nuclei of the iron peak are produced, has revealed a number of potential improvements in the treatment of this ultimate stage of astrophysical nuclear energy generation. We will discuss results gleaned from simulation work done with a large nuclear network (300 nuclei and 3000 reactions) and from independent calculations of equilirium abundance distributions, which offer new insights into the quasi-equilibrium mechanism and the approach to NSE. We find that the degree to which the matter has been neutronized is of great importance, not only to the final products, but also to the rate of energy generation and the membership of the quasi-equilibrium groups. Furthermore, we find that, as a result of quasi-equilibrium, incomplete silicon burning results in neutron richness among the isotopes of the iron group much larger than the global neutronization would indicate. We will discuss methods which use this quasi-equilibrium mechanism to preserve the most important features of the large nuclear network calculations at a significant improvement in computational speed. Such improved methods are ideally suited for hydrodynamic calculations which involve the production of iron peak nuclei, where the larger network calculation proves unmanageable.

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