The Role of Primary 16O as a Neutron Poison in AGB stars and Fluorine primary production at Halo Metallicities

TL;DR

This paper investigates how primary 16O acts as a neutron poison in AGB stars, affecting s-element synthesis at Halo metallicities, and explores primary fluorine production boosted by proton captures, with implications for stellar nucleosynthesis models.

Contribution

It reveals the significant role of primary 16O as a neutron poison in AGB stars at Halo metallicities and updates nucleosynthesis understanding after correcting a computational bug.

Findings

Primary 16O significantly affects s-element production at high 13C-pocket efficiencies.

Proton captures enhance primary fluorine production without impacting s-elements.

The bug correction alters previous conclusions about neutron poisoning in AGB nucleosynthesis.

Abstract

The discovery of a historical bug in the s-post-process AGB code obtained so far by the Torino group forced us to reconsider the role of primary 16O in the 13C-pocket, produced by the 13C(a, n)16O reaction, as important neutron poison for the build up of the s-elements at Halo metallicities. The effect is noticeable only for the highest 13C-pocket efficiencies (cases ST*2 and ST). For Galactic disc metallicities, the bug effect is negligible. A comparative analysis of the neutron poison effect of other primary isotopes (12C, 22Ne and its progenies) is presented. The effect of proton captures, by 14N(n, p)14C, boosts a primary production of Fluorine in Halo AGB stars, with [F/Fe] comparable to [C/Fe], without affecting the s-elements production.