Weak-interaction mediated rates on iron isotopes for presupernova evolution of massive stars

TL;DR

This paper presents improved microscopic calculations of weak-interaction rates for iron isotopes, crucial for modeling presupernova evolution of massive stars, incorporating experimental deformation data and comparing results with existing models.

Contribution

The study introduces refined pn-QRPA calculations of Gamow-Teller strength distributions for iron isotopes, including six weak-interaction rates, with experimental deformation data enhancing accuracy.

Findings

Electron capture and neutrino cooling rates agree with large-scale shell model results.

Beta decay rates are significantly suppressed compared to previous models.

Incorporation of experimental deformation improves the reliability of weak-interaction rate calculations.

Abstract

During the presupernova evolution of massive stars, the isotopes of iron, $^{54,55,56}$Fe, are advocated to play a key role inside the cores primarily decreasing the electron-to-baryon ratio ($Y_{e}$) mainly via electron capture processes thereby reducing the pressure support. Electron decay and positron capture on $^{55}$Fe, on the other hand, also has a consequential role in increasing the lepton ratio during the silicon burning phases of massive stars. The neutrinos and antineutrinos produced, as a result of these weak-interaction reactions, are transparent to the stellar matter and assist in cooling the core thereby reducing the entropy. The structure of the presupernova star is altered both by the changes in $Y_{e}$ and the entropy of the core material. The aim of this paper is to report the improved microscopic calculation of Gamow-Teller (GT$_{\pm}$) strength distributions of these key isotopes of iron using the pn-QRPA theory. The main improvement comes from the incorporation of experimental deformation values for these nuclei. Additionally six different weak-interaction rates, namely electron & positron capture, electron & positron decay, and, neutrino & antineutrino cooling rates, were also calculated in presupernova matter. The calculated electron capture and neutrino cooling rates due to isotopes of iron are in good agreement with the large-scale shell model (LSSM) results. The calculated beta decay rates, however, are suppressed by three to five orders of magnitude.