Nucleosynthesis in Neutrino‐driven Winds. II. Implications for Heavy Element Synthesis

During the first 20 seconds of its life, the enormous neutrino luminosity ofa neutron star drives appreciable mass loss from its surface. Thisneutrino-driven wind has been previously identified as a likely site for ther-process. Qian & Woosley (1996) have derived, both analytically andnumerically, the physical conditions relevant for heavy element synthesis inthe wind. These conditions include the entropy (S), the electron fraction (Ye),the dynamic time scale, and the mass loss rate. Here we explore theimplications of these conditions for nucleosynthesis. We find that the standardwind models derived in that paper are inadequate to make the r-process, thoughthey do produce some rare species above the iron group. We further determinethe general restrictions on the entropy, the electron fraction, and the dynamictime scale that are required to make the r-process. In particular, we derivefrom nuclear reaction network calculations the conditions required to give asufficient neutron-to-seed ratio for production of the platinum peak. Theseconditions range from Ye = 0.2 and S < 100 per baryon for reasonable dynamictime scales of 0.001-0.1 s, to Ye = 0.4-0.495 and S > 400 per baryon for adynamic time scale of 0.1 s. These conditions are also derived analytically toillustrate the physics determining the neutron-to-seed ratio.Comment: 36 pages, 11 Postscript figures, AASTe