Stellar Weak Rates and Mass Fractions of 20 Most Important $fp$-shell Nuclei with $A < 65$

TL;DR

This paper calculates stellar weak interaction rates and mass fractions for 20 key $fp$-shell nuclei with $A<65$, using microscopic models and nuclear statistical equilibrium, to improve supernova simulations.

Contribution

It introduces a microscopic calculation of weak rates without Brink-Axel hypothesis and compares mass fractions with previous models, enhancing stellar evolution modeling.

Findings

Mass fractions agree well with previous results, with some differences up to a factor of 4.

Weak rates are larger at high core temperatures compared to shell model calculations.

The study covers a wide range of densities and temperatures relevant for presupernova evolution.

Abstract

This work presents stellar weak rates and mass fractions of 20 most important electron capture (ec) and beta decay (bd) nuclei with $A < 65$ according to a recent study during the presupernova evolution of massive stars. The mass fractions of these nuclei were calculated using the Sahas equation which assumes nuclear statistical equilibrium for a set of initial conditions ($T_9$, $\rho$ and $Y_e$) that represents the trajectory which a massive stars central region takes after its silicon core burns. Our computed mass fractions were found in decent comparison in most cases, and up to a factor 4 difference was noted when compared with the Independent Particle Model results. The weak interaction (ec and bd) rates were calculated in a totally microscopic fashion using the proton neutron quasiparticle random phase ap proximation model and without assuming the Brink Axel hypothesis. The rates were computed for a wide range of density ($10$-$10^{11}$) g/cm$^3$ and temperature (0.01-30) GK. In comparison with large scale shell model, our computed rates were found bigger at high values of core temperature. The current study may contribute in a more realistic simu lation of stellar evolution processes and modeling of core collapse supernovae.