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The Astrophysical Journal


The American Astronomical Society


We consider two questions of importance to the science of nucleosynthesis: (1) Can 56Fe, rather than 56Ni, have been synthesized in its observed ratio to 28Si within a silicon-burning quasi-equilibrium? (2) What accounts for the large abundance of 58Ni? The answer to the first question is in the negative, be- cause a large overabundance of other neutron-rich nuclei, especially 54Fe or 52Cr, appears in the quasi- equilibrium distributions which yield the observed abundance ratio for 56Fe/28Si. The large 58Ni abun- dance seems to imply one of the following: (1) the iron peak is synthesized in an e-process dominated by "Ni, in which case the lighter a-particle nuclei are probably synthesized in a cooler mass zone of the same object; (2) the iron peak represents a superposition of at least two considerably different types of equilibrium processes, one accounting for "Ni and the other accounting for "Fe and 58Ni; or (3) 58Ni is due to the p-process. Determination of the proper means of production of 58Ni is one of the most im- portant problems associated with nucleosynthesis today.