Magnetic and non-magnetic AGB mixing for s-processing

¹ Department of Physics and Geology, University of Perugia, Via A. Pascoli snc, I-06125 Perugia, Italy
² INFN Section of Perugia, Via A. Pascoli snc, I-06125 Perugia, Italy

^* e-mail: maurizio.busso@pg.infn.it

Published online: 3 February 2023

Abstract

I outline a few features of recent models for the formation of the neutron source ¹³C(α,n)¹⁶O in low mass stars (1 ≲ M/M_⊙ ≲ 3, LMS ) ascendingfor the second time the Red Giant Branch, generally called Asymptotic Giant Branch, or AGB stars. I also briefly outline the nucleosynthesis results obtained trough them. The mentioned models consider the physical structure below the frequent downward extensions of the convective envelope into the He-intershell (the so-called third dredge-up or TDU episodes). There, the conditions are such that the occurrence of further mixing is strongly facilitated, due to the minimal temperature gradient. A way to induce proton mixing from the envelope (certainly not the only one) arises whenever the ambient magnetic fields expected for LMS promote the buoyancy of strongly magnetized flux tubes. I review some characteristics of the ensuing mixing episodes, mentioning how different hydrodynamical processes might yield similar effects, thus encouraging stellar physicists to verify in more detail this possibility.