A mechanism to account for well known peculiarities of low mass AGB star nucleosynthesis

Sara Palmerini,Diego Vescovi,Maurizio Busso,Oscar Trippella,M La Cognata,C Spitaleri,S Palmerini,R.G Pizzone,M Lattuada

doi:10.1051/epjconf/201716501039

Abstract

We present here the application of a model for a mass circulation mechanism induced by the stellar magnetic field to study peculiar aspects of AGB star nucleosynthesis. The mixing scheme is based on a previously suggested magnetic-buoyancy process [1, 2] and here shown to account adequately for the formation of the 13 C neutron source for s-processes. In particular our analysis results are focused on addressing the constrains to AGB nucleosynthesis coming from the isotopic composition of presolar grains recovered in meteorites. It turns out that n -captures driven by the magnetically-induced mixing can account for the isotopic abundance ratios of s -elements recorded.

Highlights

The Asymptotic Giant Branch (AGB) phase is a late stage of evolution of low mass stars (M≤6M ) that is well known to be site for the production of nuclei heavier than Fe via the slow neutron capture process (s−process)
Since the 22Ne(α,n)25Mg can not be efficiently burnt in stars with mass smaller than 3M because of the low temperatures, the s−elements from Sr to Pb observed in low mass AGB stars have to be produced trough the capture of neutrons provided by the 13C source
In particular [1] demonstrated that in red giant stars magnetized parcels of matter might arrange themselves in buoyant structures that expand from radiative layers to convective envelopes. [2] shown this process to be a reliable trigger for the proton injection in the He-rich region during the TDU, for the 13C − pocket formation. Even if in this scenario the number of mixed protons is smaller than what usually claimed in literature [6], the model well reproduces the s-element abundances measured in young open clusters and on C-rich AGB stars

Summary

Introduction

The Asymptotic Giant Branch (AGB) phase is a late stage of evolution of low mass stars (M≤6M ) that is well known to be site for the production of nuclei heavier than Fe via the slow neutron capture process (s−process). Even if in this scenario the number of mixed protons is smaller than what usually claimed in literature [6], the model well reproduces the s-element abundances measured in young open clusters and on C-rich AGB stars.

Results

Conclusion