Production of the light p-process nuclei in neutrino-driven winds

Recent studies of nucleosynthesis that occurs in the neutrino-driven wind following the delayed explosion of a Type II or Ib supernova have provided a promising site for the synthesis of the r-process isotopes. One worrisome aspect of these models is a large overproduction of N = 50 (closed neutron shell) nuclei in about 0.01 M(.) of the ejecta with entropy per baryon S/(N(A)k) approximate to 50 originating before the r-process epoch, at times t less than or similar to 1 s after core bounce. This overproduction is a consequence of the low electron fraction (Y-e approximate to 0.46) employed in these calculations. We have found that raising Y-e in the wind at this time to approximate to 0.485 cures the difficulty. The problematic nucleosynthesis disappears and is replaced by the moderate production of Ge-70 and some interesting light p-process nuclei, Se-74, Kr-78, Sr-84, and Mo-92, thus potentially turning a major shortcoming of this model into a success. The early neutrino-heated ejecta must have Y-e greater than or similar to 0.484 to effect a cure of the N = 50 overproduction problem and produce the light p-nuclei up to Mo-92. If Y-e greater than or similar to 0.488, production of light p-nuclei is lost, but the N = 50 overproduction is still avoided. In addition, Zn-64 is produced in amounts that could be important for galactic chemical evolution. It is interesting that the r-process and some light p-process nuclei may be coproduced. We are also able to place approximate limits on the mass a typical Type II supernova can eject as a function of Y-e. In particular, the ejected mass having Y-e less than or similar to 0.47 must be less than or similar to 10(-4) M(.).