NUCLEOSYNTHETIC CONSTRAINTS ON THE MASS OF THE HEAVIEST SUPERNOVAE

We explore the sensitivity of nucleosynthesis in massive stars to the truncation of supernova explosions above a certain mass. It is assumed that stars of all masses contribute to nucleosynthesis by their pre-explosive winds, but above a certain limiting main sequence mass, M-BH, the presupernova star becomes a black hole and ejects nothing more. The solar abundances from oxygen to atomic mass 90 are fit quite well assuming no cutoff at all, i.e., by assuming all stars up to 120 M-circle dot make successful supernovae. Little degradation in the fit occurs if M-BH is reduced to 25 M-circle dot. If this limit is reduced further however, the nucleosynthesis of the s-process declines precipitously and the production of species made in the winds, e. g., carbon, becomes unacceptably large compared with elements made in the explosion, e. g., silicon and oxygen. By varying uncertain physics, especially the mass loss rate for massive stars and the rate for the Ne-22(alpha, n)Mg-25 reaction rate, acceptable nucleosynthesis might still be achieved with a cutoff as low as 18 M-circle dot. This would require, however, a supernova frequency three times greater than the fiducial value obtained when all stars explode in order to produce the required O-16. The effects of varying M-BH on the nucleosynthesis of Fe-60 and Al-26, the production of helium as measured by Delta Y/Delta Z, and the average masses of compact remnants are also examined.