Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities

TL;DR

This study investigates how magnetic buoyancy influences fluorine production in AGB stars across different metallicities, showing that magnetic mixing reduces fluorine overproduction at low metallicities, aligning models with observations.

Contribution

It introduces magnetic buoyancy as a key process in AGB star models, improving fluorine nucleosynthesis predictions across metallicities.

Findings

Magnetic buoyancy reduces fluorine overproduction at low metallicities.

Models with magnetic mixing agree with observed fluorine abundances.

Fluorine mainly produced from secondary ${}^{14}$N during thermal pulses.

Abstract

Asymptotic giant branch (AGB) stars are considered to be among the most significant contributors to the fluorine budget in our Galaxy. While at close-to-solar metallicity observations and theory agree, at lower metallicities stellar models overestimate the fluorine production with respect to heavy elements. We present ${}^{19}$F nucleosynthesis results for a set of AGB models with different masses and metallicities in which magnetic buoyancy acts as the driving process for the formation of the ${}^{13}$C neutron source (the so-called ${}^{13}$C pocket). We find that ${}^{19}$F is mainly produced as a result of nucleosynthesis involving secondary ${}^{14}$N during convective thermal pulses, with a negligible contribution from the ${}^{14}$N present in the ${}^{13}$C pocket region. A large ${}^{19}$F production is thus prevented, resulting in lower fluorine surface abundances. As a consequence, AGB stellar models with magnetic-buoyancy-induced mixing at the base of the convective envelope well agree with available fluorine spectroscopic measurements at both low and close-to-solar metallicity.