The Hydrodynamic Environment for the s Process in the He-Shell Flash of AGB Stars

TL;DR

This paper presents 3D hydrodynamic simulations of He-shell flash convection in AGB stars, exploring the dynamics of neutron production and the role of the convection boundary during H-ingestion episodes, with implications for the s-process nucleosynthesis.

Contribution

It introduces a global 3D simulation approach for the entire He-shell flash convection zone, demonstrating the feasibility of explicit treatment over the anelastic approximation.

Findings

Convection is dominated by large cells filling more than an octant.

Simulations cover nearly ten convective turn-over times.

The approach captures the convection zone's extent and dynamics effectively.

Abstract

The He-shell flash convection in AGB stars is the site for the high-temperature component of the s-process in low- and intermediate mass giants, driven by the Ne22 neutron source. [...] The upper convection boundary plays a critical role during the H-ingestion episode that may lead to neutron-bursts in the most metal-poor AGB stars. We address these problems through global 3-dimensional hydrodynamic simulations including the entire spherical He-shell flash convection zone (as oposed to the 3D box-in-a-star simulations). An important aspect of our current effort is to establish the feasibility of our appoach. We explain why we favour the explicit treatment over the anelastic approximation for this problem. The simulations presented in this paper use a Cartesian grid of 512^3 cells and have been run on four 8-core workstations for four days to simulate ~5000s, which corresponds to almost ten convective turn-over times. The convection layer extends radially at the simulated point in the flash evolution over 7 H_p pressure scale-heights and exceeds the size of the underlying core. Convection is dominated by large convective cells that fill more than an entire octant. [...]