Fluorine nucleosynthesis and s-processing in AGB stars driven by magnetic-buoyancy mixing

¹ Goethe University Frankfurt, Max-von-Laue-Strasse 1, Frankfurt am Main 60438, Germany
² INAF, Observatory of Abruzzo, Via Mentore Maggini snc, 64100 Teramo, Italy
³ INFN, Section of Perugia, Via A. Pascoli snc, 06123 Perugia, Italy
⁴ Department of Physics and Geology, University of Perugia, via A. Pascoli snc, 06123 Perugia, Italy
⁵ University of Granada, Departamento de Fisica Teorica y del Cosmos, 18071 Granada, Spain

^* e-mail: vescovi@iap.uni-frankfurt.de

Published online: 24 February 2022

Abstract

Asymptotic giant branch (AGB) stars are thought to be among the most important sources of fluorine in our Galaxy. While observations and theory agree at close-to-solar metallicity, stellar models overestimate fluorine production in comparison to heavy elements at lower metallicities. We present predictions for ¹⁹F abundance for a set of AGB models with various masses and metallicities, in which magnetic buoyancy induces the formation of the ¹³C neutron source (the so-called ¹³C pocket). In our new models, fluorine is mostly created as a consequence of secondary ¹⁴N nucleosynthesis during convective thermal pulses, with a minor contribution from the ¹⁴N existing in the ¹³C pocket zone. As a result, AGB stellar models with magnetic-buoyancyinduced mixing show low ¹⁹F surface abundances which agree with fluorine spectroscopic observations at both low and near-solar metallicity.