# Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

## TL;DR

This study investigates how different mixing functions in low-mass AGB stars affect the formation of 13C pockets and the resulting s-process element abundances, highlighting the importance of stellar uncertainties over mixing details.

## Contribution

It introduces a parametric model to assess the impact of various mixing functions on s-process nucleosynthesis in AGB stars, emphasizing the role of other stellar factors.

## Key findings

- Variations in mixing functions produce similar s-process abundance results.
- Relative abundance changes are within observational error margins.
- Pb abundance is notably affected at low metallicity.

## Abstract

The production of the elements heavier than iron via slow neutron captures (the s process) is a main feature of the contribution of asymptotic giant branch (AGB) stars of low mass (< 5 Msun) to the chemistry of the cosmos. However, our understanding of the main neutron source, the 13C(alpha,n)16O reaction, is still incomplete. It is commonly assumed that in AGB stars mixing beyond convective borders drives the formation of 13C pockets. However, there is no agreement on the nature of such mixing and free parameters are present. By means of a parametric model we investigate the impact of different mixing functions on the final s-process abundances in low-mass AGB models. Typically, changing the shape of the mixing function or the mass extent of the region affected by the mixing produce the same results. Variations in the relative abundance distribution of the three s-process peaks (Sr, Ba, and Pb) are generally within +/-0.2 dex, similar to the observational error bars. We conclude that other stellar uncertainties - the effect of rotation and of overshoot into the C-O core - play a more important role than the details of the mixing function. The exception is at low metallicity, where the Pb abundance is significantly affected. In relation to the composition observed in stardust SiC grains from AGB stars, the models are relatively close to the data only when assuming the most extreme variation in the mixing profile.