Nucleosynthesis below A = 100 in Massive Stars

Abstract

The production of nuclei up to and including the weak s-process component at A B 60È90 is calculated for all stages of stable and explosive nuclear burning in stars of 15, 20, and 25 with initial M _ solar metallicity. An extended nuclear reaction network of 480 isotopes is employed along with approximately two dozen recent revisions to key nuclear reaction rates. As noted previously, the new rates suggest a greatly diminished production of 17O and 18O in massive stars. 22Ne is also moderately enhanced. We Ðnd that a combination of preexplosive s-process, c-process, and (mild) r-processes in massive stars gives a consistently solar production of almost all isotopes from mass 64 through 90. However, even after the late stages of evolution are complete and the explosion is over, this same group of elements is overproduced compared to what is needed for the Sun, especially in the 25 model. M _