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

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.