The impact of (n,$\gamma$) reaction rate uncertainties of unstable isotopes near $N=50$ on the i process nucleosynthesis in He-shell flash white dwarfs

TL;DR

This study assesses how uncertainties in neutron capture reaction rates of unstable isotopes near N=50 influence i-process nucleosynthesis predictions in He-shell flash white dwarfs, finding large uncertainties comparable to observational errors.

Contribution

It quantifies the impact of nuclear physics uncertainties on i-process element predictions, highlighting key isotopes affecting abundance outcomes.

Findings

Uncertainties in neutron capture rates can exceed a factor of 20.

Model predictions are consistent with observations within these uncertainties.

Key isotopes affecting abundances include $^{85}$Br, $^{86}$Br, $^{87}$Kr, and others.

Abstract

The first peak s-process elements Rb, Sr, Y and Zr in the post-AGB star Sakurai's object (V4334 Sagittarii) have been proposed to be the result of i-process nucleosynthesis in a post-AGB very-late thermal pulse event. We estimate the nuclear physics uncertainties in the i-process model predictions to determine whether the remaining discrepancies with observations are significant and point to potential issues with the underlying astrophysical model. We find that the dominant source in the nuclear physics uncertainties are predictions of neutron capture rates on unstable neutron rich nuclei, which can have uncertainties of more than a factor 20 in the band of the i-process. We use a Monte Carlo variation of 52 neutron capture rates and a 1D multi-zone post-processing model for the i-process in Sakurai's object to determine the cumulative effect of these uncertainties on the final elemental abundance predictions. We find that the nuclear physics uncertainties are large and comparable to observational errors. Within these uncertainties the model predictions are consistent with observations. A correlation analysis of the results of our MC simulations reveals that the strongest impact on the predicted abundances of Rb, Sr, Y and Zr is made by the uncertainties in the (n,$\gamma$) reaction rates of $^{85}$Br, $^{86}$Br, $^{87}$Kr, $^{88}$Kr, $^{89}$Kr, $^{89}$Rb, $^{89}$Sr, and $^{92}$Sr. (abridged)