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

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.

9 pages, 4 figures, 1 table. Accepted for publication on ApJL

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Cited by in corpus (10)

• Direct measurement of the 13C(α,n)16O cross section into the s-process Gamow peak
• s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints
• The Gaia-ESO Survey: A new approach to chemically characterising young open clusters II. Abundances of the neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce
• Presolar grain isotopic ratios as constraints to nuclear and stellar parameters of AGB nucleosynthesis
• Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities
• Exploring the s-process history in the Galactic disk: Cerium abundances and gradients in Open Clusters from the OCCAM/APOGEE sample
• Constraints on stellar rotation from the evolution of Sr and Ba in the Galactic halo
• Magnetic-buoyancy-induced mixing in AGB Stars: a theoretical explanation of the non-universal [Y/Mg]-age relation
• Slow Neutron-Capture Process: Low-mass AGB stars and presolar silicon carbide grains
• Presolar Silicon Carbide Grains of Types Y and Z: Their Strontium and Barium Isotopic Compositions and Stellar Origins