Alpha-constrained QSE Nucleosynthesis in High-entropy and Fast-expanding Material

Abstract

We investigate the nucleosynthesis process in high-entropy ($s/k_{\mathrm{B}}\gtrsim 100$) and very fast-expanding (${\tau }_{\exp }\sim 10^{-3}\mathrm{s}$) materials. In such a material with the electron fraction near 0.5, an interesting nucleosynthesis process occurs. In this process, the abundance distribution of heavy-nuclei of $A>100$ achieve quasi-statistical equilibrium (QSE) at high temperature and the abundances are frozen at the end of the nucleosynthesis. We explain this abundance distribution using the "alpha-constrained QSE" abundances formulated in this paper. We demonstrate that this nucleosynthesis would occur in neutrino-driven winds from massive proto-neutron stars in hypernovae, where $A\sim 140$ $p$-nuclei are synthesized.

Comments: 10 pages, 17 figures. Accepted for publication in ApJ