Effects of nuclear cross sections on ${}^{19}$F nucleosynthesis at low metallicities

Abstract

The origin of fluorine is a longstanding problem in nuclear astrophysics. It is widely recognized that Asymptotic Giant Branch (AGB) stars are among the most important contributors to the Galactic fluorine production. In general, extant nucleosynthesis models overestimate the fluorine production by AGB stars with respect to observations. In this paper we review the relevant nuclear reaction rates involved in the fluorine production/destruction. We perform this analysis on a model with initial mass M=2 M${}_{\odot }$ and Z=0.001. We found that the major uncertainties are due to the ${}^{13}$C($\alpha$,n)${}^{16}$O, the ${}^{19}$F($\alpha$,p)${}^{22}$Ne and the ${}^{14}$N(p,$\gamma$)${}^{15}$O reactions. A change of the corresponding reaction rates within the present experimental uncertainties implies surface ${}^{19}$F variations at the AGB tip lower than 10\%. For some $\alpha$ capture reactions, however, larger variations in the rates of those processes cannot be excluded. Thus, we explore the effects of the variation of some $\alpha$ capture rates well beyond the current published uncertainties. The largest ${}^{19}$F variations are obtained by varying the ${}^{15}$N($\alpha$,$\gamma$)${}^{19}$F and the ${}^{19}$F($\alpha$,p)${}^{22}$Ne reactions. The analysis of some $\alpha$ capture processes assuming a wider uncertainty range determines ${}^{19}$F abundances in better agreement with recent spectroscopic fluorine measurements at low metallicity. In the framework of the latter scenario the ${}^{15}$N($\alpha$,$\gamma$)${}^{19}$F and the ${}^{19}$F($\alpha$,p)${}^{22}$Ne reactions show the largest effects on fluorine nucleosynthesis. The presence of poorly known low energy resonances make such a scenario, even if unlikely, possible. We plan to directly measure these resonances.

9 pages, 1 figure Accepted for publication on Astronomy & Astrophysics

References in corpus (8)

• Heavy elements in Globular Clusters: the role of AGB stars
• First Direct Measurement of the ^{17}O(p,γ)^{18}F Reaction Cross-Section at Gamow Energies for Classical Novae
• s-Processing in AGB Stars Revisited. I. Does the Main Component Constrain the Neutron Source in the 13C-Pocket?
• A Method to Derive the Absolute Composition of the Sun, the Solar System and the Stars
• Constraining the S factor of 15N(p,g)16O at Astrophysical Energies
• The Chemical Evolution of Fluorine in the Bulge - High-resolution K-band spectra of giants in three fields
• Lifetime measurement of the 6792 keV state in 15O, important for the astrophysical S factor extrapolation in 14N(p,g)15O
• The thermonuclear rate for the 19F(a,p)22Ne reaction at stellar temperatures

Cited by in corpus (5)

• Fluorine in the Solar neighborhood: No evidence for the neutrino process
• Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities
• Fluorine in the solar neighborhood: modelling the Galactic thick and thin discs
• The CARMENES search for exoplanets around M dwarfs: Rubidium abundances in nearby cool stars
• Chemical Evolution of Fluorine in the Milky Way