Thermonuclear 17O(n,gamma)18O reaction rate and its astrophysical implications

TL;DR

This paper presents a new, more accurate rate for the $^{17}$O(n,$\gamma$)$^{18}$O reaction, with significant implications for stellar nucleosynthesis models, especially in the s-process, while showing minimal impact on r-process scenarios.

Contribution

The study provides a comprehensive calculation of the $^{17}$O(n,$\gamma$)$^{18}$O reaction rate up to 2 GK, including uncertainties, and explores its astrophysical implications in various stellar models.

Findings

The new reaction rate is up to 80 times larger than previous estimates in certain temperature ranges.

Enhanced $^{17}$O($n$,$\gamma$)$^{18}$O rate significantly increases $^{18}$O and $^{19}$F abundances in AGB stars.

Impact on r-process is minimal, with some effects observed only when fission recycling is neglected.

Abstract

A new thermonuclear $^{17}$O($n$,$\gamma$)$^{18}$O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have firstly calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte-Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 $\sim$ 2 GK, by up to a factor of $\sim$80. The astrophysical impacts of our rate have been examined in both $s$-process and $r$-process models. In our main $s$-process model which simulates flash-driven convective mixing in metal deficient asymptotic giant branch stars, both $^{18}$O and $^{19}$F abundances in interpulse phases are enhanced dramatically by factors of $\sim 20$--$40$ due to the new larger $^{17}$O($n$,$\gamma$)$^{18}$O rate. It shows, however, that this reaction hardly affects the weak $s$-process in massive stars since the $^{17}$O abundance never becomes significantly large in the massive stars. For the $r$-process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting "loophole" effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model, however, these significant differences are almost completely washed out if the fission recycling is considered.