Nucleosynthesis of Light Elements and Heavyr‐Process Elements through the ν‐Process in Supernova Explosions

Abstract

We study the nucleosynthesis of the light elements 7Li and 11B and the r-process elements in Type II supernovae from the point of view of supernova neutrinos and Galactic chemical evolution. We investigate the influence of the luminosity and average energy (temperature) of supernova neutrinos on these two nucleosynthesis processes. Common models of the neutrino luminosity, which is parameterized by the total energy Eν and decay time τν, and neutrino temperature are adopted to understand both processes. We adopt the model of the supernova explosion of a 16.2 M☉ star, which corresponds to SN 1987A, and calculate the nucleosynthesis of the light elements by postprocessing. We find that the ejected masses of 7Li and 11B are roughly proportional to the total neutrino energy and are weakly dependent on the decay time of the neutrino luminosity. As for the r-process nucleosynthesis, we adopt the same models of the neutrino luminosity in the neutrino-driven wind models of a 1.4 M☉ neutron star. We find that the r-process nucleosynthesis is affected through the peak neutrino luminosity, which depends on Eν/τν. The observed r-process abundance pattern is better reproduced at a low peak neutrino luminosity. We also discuss the unresolved problem of the overproduction of 11B in the Galactic chemical evolution of the light elements. We first identify that the ejected mass of 11B is a factor of 2.5-5.5 overproduced in Type II supernovae when one adopts neutrino parameters similar to those in previous studies, i.e., Eν = 3.0 × 1053 ergs, τν = 3 s, and a neutrino temperature T = T = 8.0 MeV/k. We have to assume Eν ≤ 1.2 × 1053 ergs to avoid the overproduction of 11B, which is too small to accept in comparison to the 3.0 × 1053 ergs deduced from the observation of SN 1987A. We here propose to reduce the temperatures of νμ,τ and μ,τ to 6.0 MeV/k in a model with Eν ~ 3.0 × 1053 ergs and τν ~ 9 s. This modification of the neutrino temperature is shown to resolve the overproduction problem of 11B while still keeping a successful r-process abundance pattern.