Magnetic-buoyancy Induced Mixing in AGB Stars: Presolar SiC Grains

TL;DR

This study uses presolar SiC grain isotope data to calibrate magnetic-field-induced mixing models in AGB stars, improving understanding of stellar mixing processes and matching observed isotopic ratios.

Contribution

It introduces a new magnetic mixing model in AGB stars calibrated with presolar grain data, enhancing prior stellar mixing theories.

Findings

Model successfully fits isotope ratios of Ni, Sr, Zr, Mo, Ba

Magnetic field configuration can explain observed isotopic compositions

Provides a new calibration method for stellar mixing models

Abstract

Isotope ratios can be measured in presolar SiC grains from ancient Asymptotic Giant Branch (AGB) stars at permil-level (0.1\%) precision. Such precise grain data permit derivation of more stringent constraints and calibrations on mixing efficiency in AGB models than traditional spectroscopic observations. In this paper we compare SiC heavy-element isotope ratios to a new series of FRUITY models that include the effects of mixing triggered by magnetic fields. Based on 2D and 3D simulations available in the literature, we propose a new formulation, upon which the general features of mixing induced by magnetic fields can be derived. The efficiency of such a mixing, on the other hand, relies on physical quantities whose values are poorly constrained. We present here our calibration by comparing our model results with the heavy-element isotope data of presolar SiC grains from AGB stars. We demonstrate that the isotopic compositions of all measured elements (Ni, Sr, Zr, Mo, Ba) can be simultaneously fitted by adopting a single magnetic field configuration in our new FRUITY models.