The 13C Pocket in Low Mass AGB Stars

TL;DR

This paper reviews the progress over 50 years in understanding the s process nucleosynthesis in low-mass AGB stars, focusing on the formation of the 13C pocket and its role in heavy element production.

Contribution

It provides a comprehensive review of the physical processes, neutron sources, and mixing mechanisms that enable s process nucleosynthesis in low-mass AGB stars.

Findings

Identification of main neutron sources for s process

Role of convective mixing in 13C pocket formation

Advances in modeling AGB star nucleosynthesis

Abstract

It is well known that thermally pulsing Asymptotic Giant Branch stars with low mass play a relevant role in the chemical evolution. They have synthesized about 30% of the galactic carbon and provide an important contribution to the nucleosynthesis of heavy elements (A>80). The relevant nucleosynthesis site is the He-rich intermediate zone (less than 10^{-2} Msun), where alpha(2alpha,gamma)12C reactions and slow neutron captures on seed nuclei essentially iron) take place. A key ingredient is the interplay between nuclear processes and convective mixing. It is the partial overlap of internal and external convective zones that allows the dredge-up of the material enriched in C and heavy elements. We review the progresses made in the last 50 years in the comprehension of the s process in AGB stars, with special attention to the identification of the main neutron sources and to the particular physical conditions allowing this important nucleosynthesis.