s-Processing in AGB Stars Revisited. I. Does the Main Component Constrain the Neutron Source in the 13C-Pocket?

Abstract

Slow neutron captures at A$\gtrsim$ 85 are mainly guaranteed by the reaction 13C($\alpha$,n)16O in AGB stars, requiring proton injections from the envelope. These were so far assumed to involve a small mass ($\lesssim 10^{-3}$ M${}_{\odot }$), but models with rotation suggest that in such tiny layers excessive 14N hampers s-processing. Furthermore, s-element abundances in Galaxies require 13C-rich layers substantially extended in mass ($\gtrsim 4\times 10^{-3}$ M${}_{\odot }$). We therefore present new calculations aiming at clarifying those issues and at understanding if the solar composition helps to constrain the 13C "pocket" extension. We show: i) that mixing "from bottom to top" (like in magnetic buoyancy or other forced mechanisms) can form a 13C reservoir substantially larger than assumed so far, covering most of the He-rich layers; ii) that stellar models at a fixed metallicity, based on this idea reproduce the main s-component as accurately as before; iii) that they make nuclear contributions from unknown nucleosynthesis processes (LEPP) unnecessary, against common assumptions. These models also avoid problems of mixing at the envelope border and fulfil requirements from C-star luminosities. They yield a large production of nuclei below A = 100, so that 86,87Sr may be fully synthesized by AGB stars, while 88Sr, 89Y and 94Zr are contributed more efficiently than before. We finally suggest tests suitable to say a final word on the extension of the 13C pocket.

References in corpus (30)

• Neutron capture in low mass Asymptotic Giant Branch stars: cross sections and abundance signatures
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• Evolution, nucleosynthesis and yields of low mass AGB stars
• Nucleosynthesis and mixing on the Asymptotic Giant Branch. III. Predicted and observed s-process abundances
• Evolution, nucleosynthesis and yields of low mass AGB stars at different metallicities (II): the FRUITY database
• Chemistry of the Sagittarius Dwarf Galaxy: a Top-Light IMF, Outflows and the R-Process
• s-Process Nucleosynthesis in Carbon Stars
• The Kr85 s-process Branching and the Mass of Carbon Stars
• Nucleosynthesis in the Early Galaxy
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. IV. A New Sample of Open Clusters
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• s-Process in Low Metallicity Stars. I. Theoretical Predictions
• s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars
• The 12C + 12C reaction and the impact on nucleosynthesis in massive stars
• The s-Process in Rotating Asymptotic Giant Branch Stars
• The effects of rotation on the s-process nucleosynthesys in Asymptotic Giant Branch stars
• Enhanced production of barium in low-mass stars: evidence from open clusters
• Low mass AGB stellar models for 0.003 < Z < 0.02: basic formulae for nucleosynthesis calculations
• Lead: Asymptotic Giant Branch production and Galactic Chemical Evolution
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• s-Processing in the Galactic Disk. I. Super-Solar Abundances of Y, Zr, La, Ce in Young Open Clusters
• News on the s process from young open clusters
• Magneto-Thermohaline Mixing in Red Giants
• Thermohaline Mixing: Does It Really Govern the Atmospheric Chemical Composition of Low-Mass Red Giants?
• Infrared Photometry and Evolution of Mass-Losing AGB Stars I. Carbon Stars Revisited
• New determination of the 13C(a, n)16O reaction rate and its influence on the s-process nucleosynthesis in AGB stars
• Zirconium, Barium, Lanthanum and Europium Abundances in Open Clusters
• Infrared Photometry and Evolution of Mass-Losing AGB Stars. II. Luminosity and Colors of MS and S Stars
• Barium and Yttrium abundance in intermediate-age and old open clusters
• Luminosities of Carbon-rich Asymptotic Giant Branch stars in the Milky Way

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