The Reaction Rate Sensitivity of Nucleosynthesis in Type II Supernovae

We explore the sensitivity of the nucleosynthesis of intermediate masselements (28 < A < 80) in supernovae derived from massive stars to the nuclearreaction rates employed in the model. Two standard sources of reaction ratedata (Woosley et al. 1978; and Thielemann et al. 1987) are employed in pairs ofcalculations that are otherwise identical. Both include as a common backbonethe experimental reactions rates of Caughlan & Fowler (1988). Two stellarmodels are calculated for each of two main sequence masses: 15 and 25 solarmasses. Each star is evolved from core hydrogen burning to a presupernova statecarrying an appropriately large reaction network, then exploded using a pistonnear the edge of the iron core as described by Woosley & Weaver (1995). Thefinal stellar yields from the models calculated with the two rate sets arecompared and found to differ in most cases by less than a factor of two overthe entire range of nuclei studied. Reasons for the major discrepancies arediscussed in detail along with the physics underlying the two reaction ratesets employed. The nucleosynthesis results are relatively robust and lesssensitive than might be expected to uncertainties in nuclear reaction rates,though they are sensitive to the stellar model employed.Comment: Latex, 43 pages, 15 figures. To appear Aug 20, 1999 in the Astrophysical Journal Revised text, Table 2 reflects production after decay, Table 3 is new. Main results and conclusions unchange