New Neutron-Capture Site in Massive Pop III and Pop II Stars as a Source for Heavy Elements in the Early Galaxy

Abstract

We propose a new neutron-capture site in early metal-poor and metal-free stars of $\sim 20$--$30{\mathrm{M}}_{\odot }$ that results from proton ingestion in the He shell during late stages of the stars' lives. Most of the neutron capture occurs in the first $\lesssim 10^6$s following proton ingestion when ${}^{13}\mathrm{C}(\alpha ,\mathrm{n}{)}^{16}\mathrm{O}$ produces neutron densities typical of the intermediate neutron-capture process. This phase may be followed by another lasting $\gtrsim 10^7$s with ${}^{17}\mathrm{O}(\alpha ,\mathrm{n}{)}^{20}\mathrm{Ne}$ producing much lower neutron densities typical of the slow neutron-capture process. We explore the dependence of the proposed neutron-capture nucleosynthesis on the amount and time of proton ingestion, the initial metallicity, and the ensuing supernova shock. We obtain a range of heavy element abundance patterns including those attributed to the slow neutron-capture process or a combination of the slow and rapid neutron-capture processes. Our results can account for the observed ubiquity of heavy elements such as Sr and Ba in the early Galaxy and explain puzzling abundance patterns of these elements in at least some very metal-poor (VMP) stars including those of the carbon-enhanced varieties. In the latter case, the explanation by the single site proposed here differs from the existing paradigm that attributes various classes of VMP stars to enrichment by multiple different sites.

21 pages, 12 figures, Accepted for publication in the Astrophysical Journal

References in corpus (19)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Magnetorotationally driven Supernovae as the origin of early galaxy $r$-process elements?
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Production of Light Element Primary Process nuclei in neutrino-driven winds
• The intermediate neutron-capture process and carbon-enhanced metal-poor stars
• The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• Integrated Nucleosynthesis in Neutrino Driven Winds
• i-process nucleosynthesis and mass retention efficiency in He-shell flash evolution of rapidly accreting white dwarfs
• CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star
• New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34 : binarity and neutron-capture elements
• Pop III $\text{i}$-process Nucleosynthesis and the Elemental Abundances of SMSS J0313-6708 and the Most Iron-Poor Stars
• Nine New Metal-Poor Stars on the Subgiant and Red Horizontal Branches with High Levels of r-process Enhancement
• Observational Constraints on First-Star Nucleosynthesis. II. Spectroscopy of an Ultra Metal-Poor CEMP-no Star
• Are some CEMP-s stars the daughters of spinstars?
• The low Sr/Ba ratio on some extremely metal-poor stars

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• Chemical Abundances in the Ultra-Faint Dwarf Galaxies Grus I and Triangulum II: Neutron-Capture Elements as a Defining Feature of the Faintest Dwarfs
• The i-process yields of rapidly-accreting white dwarfs from multicycle He-shell flash stellar evolution models with mixing parameterizations from 3D hydrodynamics simulations
• The s Process and Beyond
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• The lanthanide fraction distribution in metal-poor stars: a test of neutron star mergers as the dominant r-process site
• Convective H-He Interactions in Massive Population III Stellar Evolution Models
• Horizons: Nuclear Astrophysics in the 2020s and Beyond
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• The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
• 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
• SPLUSJ210428.01-004934.2: An Ultra Metal-Poor Star Identified from Narrowband Photometry
• Deep underground laboratory measurement of ${}^{13}$C($\alpha$,$n$)${}^{16}$O in the Gamow windows of the $s$- and $i$-processes
• Spectroscopic study of CEMP-(s & r/s) stars- Revisiting classification criteria and formation scenarios, highlighting i-process nucleosynthesis
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• The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
• New \textsl{s}-process Mechanism in Rapidly-Rotating Massive Pop II Stars
• Neutron-capture elements in dwarf galaxies II: Challenges for the s- and i-processes at low metallicity
• The impact of (n,$\gamma$) reaction rate uncertainties of unstable isotopes on the i-process nucleosynthesis of the elements from Ba to W
• Trans-iron Ge, As, Se, and heavier elements in the dwarf metal-poor stars, HD~19445, HD~84937, HD~94028, HD~140283, and HD~160617
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• Evidence for multiple nucleosynthetic processes from carbon enhanced metal-poor stars in the Carina dwarf spheroidal galaxy
• The Pristine Inner Galaxy Survey (PIGS) VII: a discovery of the first inner Galaxy CEMP-r/s star
• Reanalysis of neutron-capture elements in the benchmark r-rich star CS 31082-001
• HCT/HESP study of two carbon stars from the LAMOST survey
• Spectroscopic study of four metal-poor carbon stars from the Hamburg/ESO Survey: On confirming the low-mass nature of their companions
• Neutron-capture elements in dwarf galaxies III: A homogenized analysis of 13 dwarf spheroidal and ultra-faint galaxies
• The peculiar abundances of HE 1005-1439. A carbon-enhanced extremely metal-poor star contaminated with products of both s-and i-process nucleosynthesis
• Chemodynamical study of two CEMP-no stars from the Hamburg/ESO Survey
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• Optical and NIR spectroscopy of cool CEMP stars to probe the nucleosynthesis in low mass AGB binary system
• The $i$-processes nucleosynthesis during the formation of He-rich hot-subdwarf stars
• Probing Massive Star Nucleosynthesis with Data on Metal-Poor Stars and the Solar System
• HR-GO II: chemical abundances of low-$E$ retrograde dynamically-tagged-groups: Revealing Thamnos as a very metal-poor substructure
• Neutron-capture elements record the ordered chemical evolution of the disc over time
• UVES analysis of red giants in the bulge globular cluster NGC 6522
• Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars