s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints

Abstract

We present post process neutron capture computations for Asymptotic Giant Branch stars of 1.5 to 3 Mo and metallicities -1.3 to 0.1. The reference stellar models are computed with the FRANEC code, using the Schwarzschild's criterion for convection. Motivations for this choice are outlined. We assume that MHD processes induce the penetration of protons below the convective boundary, when the third dredge up occurs. There, the 13C(alpha,n)16O neutron source can subsequently operate, merging its effects with those of the 22Ne(alpha,n)25Mg reaction, activated at the temperature peaks characterizing AGB stages. This work has three main scopes. i) We provide a grid of abundance yields, as produced through our MHD mixing scheme, uniformly sampled in mass and metallicity. From it, we deduce that the solar s process distribution, as well as the abundances in recent stellar populations, can be accounted for, without the need of the extra primary like contributions suggested in the past. ii) We formulate analytical expressions for the mass of the 13C pockets generated, in order to allow easy verification of our findings. iii) We compare our results with observations of evolved stars and with isotopic ratios in presolar SiC grains, also noticing how some flux tubes should survive turbulent disruption, carrying C rich materials into the winds even when the envelope is O rich. This wind phase is approximated through the G component of AGB s processing. We conclude that MHD induced mixing is adequate to drive slow neutron capture phenomena accounting for observations. Our prescriptions should permit its inclusion into current stellar evolutionary codes.

arXiv commentThe Astrophysical Journal, submitted Sep. 2, 2020; accepted, Nov. 14, 2020. 23 pages, 23 figures

References in corpus (82)

• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• Neutron capture in low mass Asymptotic Giant Branch stars: cross sections and abundance signatures
• The s Process: Nuclear Physics, Stellar Models, Observations
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• Simulations of small-scale turbulent dynamo
• 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
• Chemical evolution with rotating massive star yields: I. The solar neighbourhood and the s-process elements
• Evolution, nucleosynthesis and yields of AGB stars at different metallicities (III): intermediate mass models, revised low mass models and the ph-FRUITY interface
• Thermohaline instability and rotation-induced mixing. I - Low- and intermediate-mass solar metallicity stars up to the end of the AGB
• The s process in asymptotic giant branch stars of low metallicity and the composition of carbon-enhanced metal-poor stars
• Cool bottom processes on the thermally-pulsing AGB and the isotopic composition of circumstellar dust grains
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• NuGrid stellar data set I. Stellar yields from H to Bi for stars with metallicities Z = 0.02 and Z = 0.01
• s-Process Nucleosynthesis in Carbon Stars
• The Kr85 s-process Branching and the Mass of Carbon Stars
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Neutron Capture Elements in s-Process-Rich, Very Metal-Poor Stars
• Chemical evolution with rotating massive star yields II. A new assessment of the solar s- and r- process components
• Magnitudes and Timescales of Total Solar Irradiance Variability
• s-Process in Low Metallicity Stars. III. Individual analysis of CEMP-s and CEMP-s/r with AGB models
• The s-Process in Rotating Asymptotic Giant Branch Stars
• The effects of rotation on the s-process nucleosynthesys in Asymptotic Giant Branch stars
• More lead stars
• Low mass AGB stellar models for 0.003 < Z < 0.02: basic formulae for nucleosynthesis calculations
• Barium & related stars and their white-dwarf companions I. Giant stars
• Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars
• Three carbon-enhanced metal-poor dwarf stars from the SDSS - Chemical abundances from CO^5BOLD 3D hydrodynamical model atmospheres
• Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars
• 3D hydrodynamical simulations of a proton ingestion episode in a low-metallicity asymptotic giant branch star
• 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
• $s$-Processing in AGB Stars Revisited. II. Enhanced ${}^{13}$C Production Through MHD-Induced Mixing
• Thermohaline Mixing: Does It Really Govern the Atmospheric Chemical Composition of Low-Mass Red Giants?
• Chemical abundances and kinematics of barium stars
• Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
• A study of the s-process in the carbon-rich post-AGB stars IRAS06530-0213 and IRAS08143-4406 on the basis of VLT-UVES spectra
• Application of a Theory and Simulation based Convective Boundary Mixing model for AGB Star Evolution and Nucleosynthesis
• Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
• On the need of the Light Elements Primary Process (LEPP)
• The Origin of Fluorine: Abundances in AGB Carbon Stars Revisited
• Magnetic-buoyancy Induced Mixing in AGB Stars: Presolar SiC Grains
• On the Need for Deep Mixing in AGB Stars of Low Mass
• MHD and deep mixing in evolved stars. 1. 2D and 3D analytical models for the AGB
• Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21 micrometer star J004441.04-732136.4
• NuGrid stellar data set - III. Updated low-mass AGB models and s-process nucleosynthesis with metallicities Z=0.01, Z=0.02 and Z=0.03
• Deep Mixing in Evolved Stars. II. Interpreting Li Abundances in RGB and AGB Stars
• The importance of the 13C(alpha,n)16O reaction in Asymptotic Giant Branch stars
• Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)
• The impact of updated Zr neutron-capture cross sections and new asymptotic giant branch models on our understanding of the s process and the origin of stardust
• Mass loss and yield uncertainty in low-mass asymptotic giant branch stars
• 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
• When binaries keep track of recent nucleosynthesis: The Zr - Nb pair in extrinsic stars as an s-process diagnostic
• Stellar models with mixing length and T(tau) relations calibrated on 3D convection simulations
• Do meteoritic silicon carbide grains originate from asymptotic giant branch stars of super-solar metallicity?
• First detection of surface magnetic fields in Post-AGB stars : the cases of U Monocerotis and R Scuti
• On metal-deficient barium stars and their link with yellow symbiotic stars
• The puzzle of the CNO isotope ratios in AGB carbon stars
• Flux-tube geometry and solar wind speed during an activity cycle
• Properties of carbon stars in the Solar neighbourhood based on Gaia DR2 astrometry
• Chemical abundance study of two strongly s-process enriched post-AGB stars in the LMC: J051213.81-693537.1 and J051848.86-700246.9
• New constraints on the major neutron source in low-mass AGB stars
• Magnetic Flares on Asymptotic Giant Branch Stars
• The lead discrepancy in intrinsically s-process enriched post-AGB stars in the Magellanic Clouds
• S stars and s-process in the Gaia era I. Stellar parameters and chemical abundances in a sub-sample of S stars with new MARCS model atmospheres
• Binary evolution along the Red Giant Branch with BINSTAR: The barium star perspective
• Stellar Population Astrophysics (SPA) with TNG. The old open clusters Collinder 350, Gulliver 51, NGC 7044, and Ruprecht 171
• s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains
• Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements
• An Abundance Analysis of the New Carbon-Rich Proto-Planetary Nebula IRAS 06530$-$0213
• Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 Msun
• Discovery of technetium- and niobium-rich S stars: the case for bitrinsic stars
• IRAS08281-4850 and IRAS14325-6428: two A-type post-AGB stars with s-process enrichment
• Abundances and Depletions of Neutron-Capture Elements in the Interstellar Medium
• Measurement of the ${}^{154}$Gd(n,$\gamma$) cross section and its astrophysical implications
• Detection of elements beyond the Ba-peak in VLT+UVES spectra of post-AGB stars
• Detection of Pb II in the Ultraviolet Spectra of Three Metal-Poor Stars
• Rotational mixing in carbon-enhanced metal-poor stars with s-process enrichment

Cited by in corpus (17)

• The s Process and Beyond
• The Gaia-ESO Survey: Age-chemical-clock relations spatially resolved in the Galactic disc
• 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
• Theoretical estimate of the half-life for the radioactive ${}^{134}$Cs and ${}^{135}$Cs in astrophysical scenarios
• The GALAH survey: Tracing the Milky Way's formation and evolution through RR Lyrae stars
• The most metal-rich stars in the universe: chemical contributions of low and intermediate mass asymptotic giant branch stars with metallicities between $0.04\le Z\le \mathrm{0.10.}$
• Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution
• Underground Measurements of Nuclear Reaction Cross-Sections Relevant to AGB Stars
• Impact of AGB stars on the chemical evolution of neutron-capture elements
• Modelling chemical clocks -- Theoretical evidences of the space and time evolution of [s/alpha] in the Galactic disc with Gaia-ESO survey
• Slow Neutron-Capture Process: Low-mass AGB stars and presolar silicon carbide grains
• Presolar grains
• Silicon Isotopic Composition of Mainstream Presolar SiC Grains Revisited: The Impact of Nuclear Reaction Rate Uncertainties
• Chemical abundances of three new Ba stars from the Keck/HIRES spectra
• Impact of $\text{T}$- and $\rho$-dependent decay rates and new (n,$\gamma$) cross sections on the $\text{s}$ process in low-mass AGB stars
• Production of n-rich nuclei in red giant stars