Nucleosynthesis of light element isotopes in evolved stars experiencing extended mixing

TL;DR

This paper models nucleosynthesis in evolved stars with extended mixing driven by magnetic buoyancy, explaining observed isotope abundances and Li spread, and compares predictions with stellar and presolar grain data.

Contribution

It introduces a magnetic buoyancy-driven mixing model that accounts for both fast and slow stellar mixing phenomena, matching observed isotope and element abundances.

Findings

Good agreement between model predictions and observed isotope ratios.

Magnetic buoyancy can explain the spread in lithium abundances.

Observational data effectively constrain model parameters.

Abstract

We present computations of nucleosynthesis in red giants and asymptotic giant branch stars of Population I experiencing extended mixing. The assumed physical cause for mass transport is the buoyancy of magnetized structures, according to recent suggestions. The peculiar property of such a mechanism is to allow for both fast and slow mixing phenomena, as required for reproducing the spread in Li abundances displayed by red giants and as discussed in an accompanying paper. We explore here the effects of this kind of mass transport on CNO and intermediatemass nuclei and compare the results with the available evidence from evolved red giants and from the isotopic composition of presolar grains of AGB origin. It is found that a good general accord exists between predictions and measurements; in this framework we also show which type of observational data best constrains the various parameters. We conclude that magnetic buoyancy, allowing for mixing at rather different speeds, can be an interesting scenario to explore for explaining together the abundances of CNO nuclei and of Li.