Low metallicity AGB models: H profile in the 13C-pocket and the effect on the s-process

TL;DR

This study investigates how variations in the hydrogen profile within the 13C-pocket of low metallicity AGB stars influence s-process nucleosynthesis, focusing on key isotopes to understand uncertainties in stellar models.

Contribution

It introduces a detailed analysis of the impact of hydrogen profile variations on s-process element production in low metallicity AGB stars, addressing a key uncertainty in stellar nucleosynthesis modeling.

Findings

Hydrogen profile variations significantly affect s-process yields.

The production of isotopes 89Y, 139La, and 208Pb varies with the hydrogen profile.

Uncertainties in the 13C-pocket formation influence nucleosynthesis predictions.

Abstract

The 13C(a, n)16O reaction is the major neutron source in low mass asymptotic giant branch (AGB) stars, where the main and the strong s process components are synthesised. After a third dredge-up (TDU) episode, 13C burns radiatively in a thin pocket which forms in the top layers of the He-intershell, by proton capture on the abundant 12C. Therefore, a mixing of a few protons from the H-rich envelope into the He-rich region is requested. However, the origin and the effciency of this mixing episode are still matter of debate and, consequently, the formation of the 13C-pocket represents a significative source of uncertainty affecting AGB models. We analyse the effects on the nucleosynthesis of the s-elements caused by the variation of the hydrogen profile in the region where the 13C-pocket forms for an AGB model with M = 2 Msun and [Fe/H] = -2.3. In particular, we concentrate on three isotopes (89Y, 139La and 208Pb), chosen as representative of the three s-process peaks.