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.
Highlights
The cosmic genesis of fluorine is one of the most intriguing problems in nuclear astrophysics
Its envelope abundance indicates a correlation with those of carbon and s-process elements and with the 13C content produced in the interiors of Asymptotic giant branch (AGB) stars [5]
The formation of a 13C pocket in AGB stars requires that some partial mixing of protons from the envelope occurs during a third dredge-up (TDU) phenomenon
Summary
The cosmic genesis of fluorine is one of the most intriguing problems in nuclear astrophysics. Spectroscopic observations of photospheric F enhancements in intrinsic AGB carbon stars [1, 2] and metal-poor extrinsic stars [3, 4] offer the sole direct observation of fluorine production. Its envelope abundance indicates a correlation with those of carbon and s-process elements and with the 13C content produced in the interiors of AGB stars [5]. It was proposed that a process resulting in the creation of an extended 13C pocket and, simultaneously, a tiny quantity of 14N, may solve the issue of 19F overproduction with respect to s-elements in low-mass metal-poor objects [4]. The formation of a 13C pocket in AGB stars requires that some partial mixing of protons from the envelope occurs during a third dredge-up (TDU) phenomenon. Stars by computing a new series of stellar models accounting for the formation of a magneticbuoyancy-induced 13C pocket
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