The R-Process Alliance: Exploring the cosmic scatter among ten r-process sites with stellar abundances

Abstract

The astrophysical origin of the rapid neutron-capture process (r-process), which produces about half of the elements heavier than iron, remains uncertain. The oldest, most metal-poor stars preserve the chemical signatures of early nucleosynthesis events and can reveal the nature of the r-process sites. We present a homogeneous chemical abundance analysis of ten r-process-enhanced, metal-poor stars that show strong enrichment in r-process elements with minimal contamination from other nucleosynthetic sources. Using high-resolution, high signal-to-noise spectra, we examined over 1400 absorption lines per star through equivalent width measurements and spectral synthesis under one-dimensional LTE assumptions with the MOOG radiative transfer code. Abundances for 54 chemical species were derived, including 29 neutron-capture elements spanning the full r-process pattern. We quantified the cosmic scatter of elemental ratios relative to Zr (light) and Eu (heavy) and found remarkably small dispersions for the rare-earth and third-peak elements, σ[La/Eu] = 0.08 dex and σ[Os/Eu] = 0.11 dex, while the light-to-heavy ratio shows slightly larger variation, σ[Zr/Eu] = 0.18 dex. A kinematic study indicates that the stars likely originated from ten distinct progenitor systems, allowing us to probe the intrinsic variation between independent r-process events. These results imply that the main r-process operates under highly uniform conditions across diverse astrophysical sites.

14 pages, 9 Appendix, 9 figures

References in corpus (100)

• The chemical composition of the Sun
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• Gaia Data Release 3: Summary of the content and survey properties
• Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
• galpy: A Python Library for Galactic Dynamics
• Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event
• The mass distribution and gravitational potential of the Milky Way
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Origin of the Heaviest Elements: the Rapid Neutron-Capture Process
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• The GALAH+ Survey: Third Data Release
• The Combined Ultraviolet, Optical, and Near-Infrared Light Curves of the Kilonova Associated with the Binary Neutron Star Merger GW170817: Unified Data Set, Analytic Models, and Physical Implications
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South
• Magnetorotationally driven Supernovae as the origin of early galaxy $r$-process elements?
• The Extremely Metal-Poor, Neutron-Capture-Rich Star CS 22892-052: A Comprehensive Abundance Analysis
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• The extreme r-element rich, iron-poor halo giant CS31082-001: Implications for the r-process site(s) and radioactive cosmochronology
• Collapsars as a major source of r-process elements
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2
• The r-Process Enriched Low Metallicity Giant HD 115444
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
• NLTE abundances of Mn in a sample of metal-poor stars
• HE0107-5240, A Chemically Ancient Star.I. A Detailed Abundance Analysis
• New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
• The Role of Fission in Neutron Star Mergers and its Impact on the r-Process Peaks
• Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy
• Explorations of the r-Processes: Comparisons between Calculations and Observations of Low-Metallicity Stars
• Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars
• Neutrino-driven wind simulations and nucleosynthesis of heavy elements
• The $R$-Process Alliance: First Release from the Southern Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617
• Silver and palladium help unveil the nature of a second r-process
• Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
• New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars
• The R-Process Alliance: First Release from the Northern Search for r-Process Enhanced Metal-Poor Stars in the Galactic Halo
• The Evolution of Early-Type Galaxies in Distant Clusters III.: M/L_V Ratios in the z=0.33 Cluster CL1358+62
• Improved Ti II log(gf) Values and Abundance Determinations in the Photospheres of the Metal-Poor Star HD 84937
• Non-LTE aluminium abundances in late-type stars
• Ionization balance of Ti in the photospheres of the Sun and four late-type stars
• APASS Landolt-Sloan BVgri photometry of RAVE stars. I. Data, effective temperatures and reddenings
• HST Observations of Heavy Elements in Metal-Poor Galactic Halo Stars
• Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres
• Deriving Stellar Effective Temperatures of Metal-Poor Stars with the Excitation Potential Method
• R-Process Nucleosynthesis in MHD Jet Explosions of Core-Collapse Supernovae
• Fe I Oscillator Strengths for the Gaia-ESO Survey
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Exploiting the Gaia EDR3 photometry to derive stellar temperatures
• Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
• Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars
• The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-Poor Star with an Extreme R-Process Enhancement of [Eu/H] = -0.14
• Fe I Oscillator Strengths for Transitions from High-lying Even-Parity Levels
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• $r$-Process Nucleosynthesis from Three-dimensional Jet-driven Core-Collapse Supernovae with Magnetic Misalignments
• The R-Process Alliance: 2MASS J09544277+5246414, the Most Actinide-Enhanced R-II Star Known
• Fast estimation of orbital parameters in Milky-Way-like potentials
• Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies
• Experimental and theoretical oscillator strengths of Mg I for accurate abundance analysis
• Chemo-dynamics of outer halo dwarf stars, including \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia candidates
• Enrichment history of r-process elements shaped by a merger of neutron star pairs
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
• Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
• From actinides to zinc: Using the full abundance pattern of the brightest star in Reticulum II to distinguish between different r-process sites
• Extreme Enhancements of r-process Elements in the Cool Metal-Poor Main-Sequence Star SDSS J2357-0052
• The lanthanide fraction distribution in metal-poor stars: a test of neutron star mergers as the dominant r-process site
• The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
• Search for transient gravitational wave signals associated with magnetar bursts during Advanced LIGO's second observing run
• 3D non-LTE line formation of neutral carbon in the Sun
• 3D non-LTE iron abundances in FG-type dwarfs
• Origin of neutron capture elements with the Gaia-ESO survey: the evolution of s- and r-process elements across the Milky Way
• Evidence for $\gtrsim 4$ Gyr timescales of neutron star mergers from Galactic archaeology
• Element abundance patterns in stars indicate fission of nuclei heavier than uranium
• Co-production of light and heavy $r$-process elements via fission deposition
• The occurrence of nitrogen-enhanced metal-poor stars: implications for the initial mass function in the early Galactic halo
• Abundance patterns of the light neutron-capture elements in very and extremely metal-poor stars
• Fe I oscillator strengths for transitions from high-lying odd-parity levels
• Even-to-Odd Barium Isotope Ratio in Selected Galactic Halo Stars
• Observational constraints on the origin of the elements. VII. NLTE analysis of Y II lines in spectra of cool stars and implications for Y as a Galactic chemical clock
• Signatures of R-process Enrichment in Supernovae from Collapsars
• Non-LTE abundances of zinc in different spectral type stars and the Galactic [Zn/Fe] trend based on quantum-mechanical data on inelastic processes in zinc-hydrogen collisions
• The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
• Nuclear correlations and the r-process
• Chemo-Dynamically Tagged Groups of CEMP Stars in the Halo of the Milky Way. I. Untangling the Origins of CEMP-$s$ and CEMP-no Stars
• The R-Process Alliance: Chemo-Dynamically Tagged Groups II. An Extended Sample of Halo $r$-Process-Enhanced Stars
• Common envelope jets supernova r-process yields can reproduce $[Eu/Fe]$ abundance evolution in the Galaxy
• The R-Process Alliance: Fifth Data Release from the Search for R-Process-Enhanced Metal-poor Stars in the Galactic Halo with the GTC
• Observational constraints on the origin of the elements. V. Non-LTE abundance ratios of [Ni/Fe] in Galactic stars and enrichment by sub-Chandrasekhar mass SNe
• MINCE I. Presentation of the project and of the first year sample
• The formation of the Milky Way halo and its dwarf satellites: A NLTE-1D abundance analysis. V. The Sextans galaxy
• An extended and refined grid of 3D STAGGER model atmospheres. Processed snapshots for stellar spectroscopy
• Chemical Evolution of R-process Elements in Stars (CERES): IV. An observational run-up of the third r-process peak with Hf, Os, Ir, and Pt
• Revisiting inelastic Cu+H collisions and the non-LTE Galactic evolution of copper
• Probing Na in giant exoplanets with ESPRESSO and 3D NLTE stellar spectra
• 3D non-LTE Ca II line formation in metal-poor FGK stars. I. Abundance corrections, radial velocity corrections, and synthetic spectra