New determination of the 13C(a, n)16O reaction rate and its influence on the s-process nucleosynthesis in AGB stars

TL;DR

This study provides a new measurement of the $^{13}$C($ ext{α}$, n)$^{16}$O reaction rate, significantly impacting s-process nucleosynthesis models in AGB stars by refining neutron source estimates.

Contribution

The paper introduces a novel determination of the $^{13}$C($ ext{α}$, n)$^{16}$O reaction rate using transfer reaction data, improving the accuracy of stellar nucleosynthesis simulations.

Findings

The new reaction rate is about twice that of previous estimates at 100 MK.

Different reaction rates have minimal impact when $^{13}$C burns radiatively.

In convective burning conditions, element abundances can vary by up to 25%.

Abstract

We present a new measurement of the $\alpha$-spectroscopic factor ($S_\alpha$) and the asymptotic normalization coefficient (ANC) for the 6.356 MeV 1/2$^+$ subthreshold state of $^{17}$O through the $^{13}$C($^{11}$B, $^{7}$Li)$^{17}$O transfer reaction and we determine the $\alpha$-width of this state. This is believed to have a strong effect on the rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction, the main neutron source for {\it slow} neutron captures (the $s$-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the $^{13}$C($\alpha$, $n$)$^{16}$O reaction. At a temperature of 100 MK our rate is roughly two times larger than that by \citet{cau88} and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected $s$-process elements and isotopic ratios. There are no changes in the final results using the different rates for the $^{13}$C($\alpha$, $n$)$^{16}$O reaction when the $^{13}$C burns completely in radiative conditions. When the $^{13}$C burns in convective conditions, as in stars of initial mass lower than $\sim$2 $M_\sun$ and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available.