A Deep Mixing Solution to the Aluminum and Oxygen Isotope Puzzles in Presolar Grains

TL;DR

This paper introduces a deep mixing model based on magnetic buoyancy in low-mass AGB stars, successfully explaining extreme isotopic compositions in presolar grains, including high 26Al levels and oxygen isotope ratios.

Contribution

It presents a novel magnetic-buoyancy driven mixing scheme that reproduces extreme isotopic ratios in presolar grains, advancing understanding of stellar nucleosynthesis processes.

Findings

Reproduces extreme 17O/16O and 18O/16O ratios in presolar grains.

Successfully explains high 26Al/27Al ratios observed in oxide grains.

Validates magnetic buoyancy as a key mixing mechanism in AGB stars.

Abstract

We present here the application of a model for a mass circulation mechanism in between the H-burning shell and the base of the convective envelope of low mass AGB stars, aimed at studying the isotopic composition of those presolar grains showing the most extreme levels of 18O depletion and high concentration of 26Mg from the decay of 26Al. The mixing scheme we present is based on a previously suggested magnetic-buoyancy process, already shown to account adequately for the formation of the main neutron source for slow neutron captures in AGB stars. We find that this scenario is also capable of reproducing for the first time the extreme values of the 17O/16O, the 18O/16O, and the 26Al/27Al isotopic ratios found in the mentioned oxide grains, including the highest amounts of 26Al there measured.