The impact of the 18F(a,p)21Ne reaction on fluorine production in AGB stars

TL;DR

This study evaluates how recent experimental data on the 18F(a,p)21Ne reaction rate affects fluorine and neon production in AGB stars, revealing significant effects only at the upper limit of the rate's uncertainty.

Contribution

It provides the first detailed analysis of the impact of the new reaction rate measurements on AGB nucleosynthesis across various metallicities.

Findings

Enhanced 19F and 21Ne production at the upper limit of the reaction rate

No significant difference using recommended or lower limit rates

Results applicable to observations of F and C-rich AGB stars and silicon carbide grains

Abstract

The recent experimental evaluation of the 18F(a,p)21Ne reaction rate, when considering its associated uncertainties, presented significant differences compared to the theoretical Hauser-Feshbach rate. This was most apparent at the low temperatures relevant for He-shell burning in asymptotic giant branch (AGB) stars. Investigations into the effect on AGB nucleosynthesis revealed that the upper limit resulted in an enhanced production of 19F and 21Ne in carbon-rich AGB models, but the recommended and lower limits presented no differences from using the theoretical rate. This was the case for models spanning a range in metallicity from solar to [Fe/H] ~ -2.3. The results of this study are relevant for observations of F and C-enriched AGB stars in the Galaxy, and to the Ne composition of mainstream silicon carbide grains, that supposedly formed in the outflows of cool, carbon-rich giant stars. We discuss the mechanism that produces the extra F and summarize our main findings.