Presolar grain isotopic ratios as constraints to nuclear and stellar parameters of AGB nucleosynthesis

Abstract

Recent models for evolved Low Mass Stars (with $M\lesssim 3M_{\odot }$), undergoing the AGB phase assume that magnetic flux-tube buoyancy drives the formation of ${}^{13}$C reservoirs in He-rich layers. We illustrate their crucial properties, showing how the low abundance of ${}^{13}$C generated below the convective envelope hampers the formation of primary ${}^{14}$N and the ensuing synthesis of intermediate-mass nuclei, like ${}^{19}$F and ${}^{22}$Ne. In the mentioned models, their production is therefore of a purely secondary nature. Shortage of primary ${}^{22}$Ne has also important effects in reducing the neutron density. Another property concerns AGB winds, which are likely to preserve C-rich subcomponents, isolated by magnetic tension, even when the envelope composition is O-rich. Conditions for the formation of C-rich compounds are therefore found in stages earlier than previously envisaged. These issues, together with the uncertainties related to several nuclear physics quantities, are discussed in the light of the isotopic admixtures of s-process elements in presolar SiC grains of stellar origin, which provide important and precise constraints to the otherwise uncertain parameters. By comparing nucleosynthesis results with measured SiC data, it is argued that such a detailed series of constraints indicates the need for new measurements of weak interaction rates in ionized plasmas, as well as of neutron-capture cross sections, especially near the N = 50 and N = 82 neutron magic numbers. Nontheless, the peculiarity of our models allows us to achieve fits to the presolar grain data of a quality so far never obtained in previously published attempts.

33 pages, 38 figures, ApJ accepted

References in corpus (25)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Chemical evolution with rotating massive star yields II. A new assessment of the solar s- and r- process components
• High-precision abundances of elements in solar-type stars. Evidence of two distinct sequences in abundance-age relations
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
• On the need of the Light Elements Primary Process (LEPP)
• Magnetic-buoyancy Induced Mixing in AGB Stars: Presolar SiC Grains
• MHD and deep mixing in evolved stars. 1. 2D and 3D analytical models for the AGB
• Re-evaluation of the ${}^{22}$Ne($\alpha ,\gamma$)${}^{26}$Mg and ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg reaction rates
• s-Processing in AGB Stars Revisited. I. Does the Main Component Constrain the Neutron Source in the 13C-Pocket?
• The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains
• s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints
• First detection of surface magnetic fields in Post-AGB stars : the cases of U Monocerotis and R Scuti
• Discovery of six new strongly magnetic white dwarfs in the 20 pc local population
• Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities
• Properties of carbon stars in the Solar neighbourhood based on Gaia DR2 astrometry
• Magnetic-buoyancy-induced mixing in AGB Stars: a theoretical explanation of the non-universal [Y/Mg]-age relation
• s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains
• On the mass and metallicity distribution of parent AGB stars of presolar SiC
• Magnetic field in IRC+10216 and other C-Rich Evolved Stars
• Discovery of technetium- and niobium-rich S stars: the case for bitrinsic stars
• Millimeter polarisation of the protoplanetary nebula OH 231.8+4.2: A follow-up study with CARMA
• Magnetic fields in circumstellar envelopes of evolved AGB stars

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• Strontium-84 Enrichments in Presolar Grains Provide First Evidence of p-process Nucleosynthesis in Core-collapse Supernovae
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