Silicon Burning. I. Neutronization and the Physics of QuasiEquilibrium
Abstract
As the ultimate stage of stellar nucleosynthesis, and the source of the iron peak nuclei, silicon burning is important to our understanding of the evolution of massive stars and supernovae. Our reexamination of silicon burning, using results gleaned from simulation work done with a large nuclear network (299 nuclei and more than 3000 reactions) and from independent calculations of equilibrium abundance distributions, offers new insights into the quasiequilibrium mechanism and the approach to nuclear statistical equilibrium. 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 quasiequilibrium groups. A small increase in the global neutronization results in much larger freeneutron fluences, increasing the abundances of more neutronrich nuclei. As a result, incomplete silicon burning results in neutron richness among the isotopes of the iron peak much larger than the global neutronization would indicate. Finally, we briefly discuss the limitations and pitfalls of models for silicon burning currently employed within hydrodynamic models. In a forthcoming paper we will present a new approximation to the full nuclear network which preserves 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.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1996
 DOI:
 10.1086/177016
 arXiv:
 arXiv:astroph/9511088
 Bibcode:
 1996ApJ...460..869H
 Keywords:

 NUCLEAR REACTIONS;
 NUCLEOSYNTHESIS;
 ABUNDANCES;
 Astrophysics
 EPrint:
 44 pages of TeX with 25 Postscript figures, uses psfig.sty, To appear in the The Astrophysical Journal, April 1 1996. Complete PostScript version of the paper is also available from http://tycho.as.utexas.edu/~raph/Publications.html