Thermonuclear reaction rate of 18O(p,gamma)19F

TL;DR

This paper provides an improved thermonuclear reaction rate for 18O(p,gamma)19F, crucial for understanding stellar nucleosynthesis and presolar grain formation, by analyzing low-energy reaction data and refining existing models.

Contribution

It offers new experimental data and a revised reaction rate for 18O(p,gamma)19F, enhancing models of stellar processes and presolar grain formation.

Findings

The resonance at 95 keV has negligible impact on the reaction rate.

The direct capture S-factor is nearly half of previous estimates at low energies.

The new reaction rate refines understanding of 18O depletion in stellar environments.

Abstract

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as "cool bottom processing" (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented.