Dependence of X-ray Burst Models on Nuclear Masses

TL;DR

This study identifies key nuclear mass uncertainties affecting X-ray burst models, highlighting specific isotopes that influence light curves and compositions, and suggests targeted experimental measurements to improve model accuracy.

Contribution

The paper pinpoints critical nuclear masses impacting X-ray burst predictions and demonstrates how reducing these uncertainties can refine astrophysical models.

Findings

Three nuclear masses affect light curves in typical bursts.

Multiple masses significantly influence final composition.

Improved mass measurements can enhance model predictions.

Abstract

X-ray burst model predictions of light curves and final composition of the nuclear ashes are affected by uncertain nuclear masses. However, not all of these masses are determined experimentally with sufficient accuracy. Here we identify remaining nuclear mass uncertainties in X-ray burst models using a one zone model that takes into account the changes in temperature and density evolution caused by changes in the nuclear physics. Two types of bursts are investigated - a typical mixed H/He burst with a limited rp-process and an extreme mixed H/He burst with an extended rp-process. When allowing for a 3$\sigma$ variation only three remaining nuclear mass uncertainties affect the light curve predictions of a typical H/He burst ($^{27}$P, $^{61}$Ga, and $^{65}$As), and only three additional masses affect the composition strongly ($^{80}$Zr, $^{81}$Zr, and $^{82}$Nb). A larger number of mass uncertainties remains to be addressed for the extreme H/He burst with the most important being $^{58}$Zn, $^{61}$Ga, $^{62}$Ge, $^{65}$As, $^{66}$Se, $^{78}$Y, $^{79}$Y, $^{79}$Zr, $^{80}$Zr, $^{81}$Zr, $^{82}$Zr, $^{82}$Nb, $^{83}$Nb, $^{86}$Tc, $^{91}$Rh, $^{95}$Ag, $^{98}$Cd, $^{99}$In, $^{100}$In, and $^{101}$In. The smallest mass uncertainty that still impacts composition significantly when varied by 3$\sigma$ is $^{85}$Mo with 16 keV uncertainty. For one of the identified masses, $^{27}$P, we use the isobaric mass multiplet equation (IMME) to improve the mass uncertainty, obtaining an atomic mass excess of -716(7) keV. The results provide a roadmap for future experiments at advanced rare isotope beam facilities, where all the identified nuclides are expected to be within reach for precision mass measurements.