An Actinide-boost Star Discovered in the Gaia-Sausage-Enceladus

Abstract

We report the discovery of an actinide-boost, very metal-poor ($\left[Fe/H\right]=-2.38$), $r$-process-enhanced ($\left[Eu/Fe\right]=0.80$) star, LAMOST J0804+5740, within the Gaia-Sausage-Enceladus (GSE). Based on the high-resolution ($R\sim 36,000and60,000$) and high signal-to-noise ratio spectra obtained with the High Dispersion Spectrograph on the Subaru Telescope, the abundances of 48 species are determined. Its $\log \epsilon (\mathrm{Th}/\mathrm{Eu})=-0.22$ establishes it as the first confirmed actinide-boost star within the GSE. Comparative analysis of its abundance pattern with theoretical $r$-process models reveals that the magnetorotationally driven jet supernova $r$-process model with $\hat{L}v$ = 0.2 provides the best fit and successfully reproduces the actinide-boost signature. Kinematic analysis of actinide-boost stars reveals that approximately two-thirds of them are classified as $\text{ex-situ}$ stars, suggesting that actinide-boost stars are more likely to originate from accreted dwarf galaxies. As the first actinide-boost star identified within the GSE, J0804+5740 will provide valuable insights into $r$-process nucleosynthesis in accreted dwarf galaxies like the GSE, especially on the production of the heaviest elements.

10 pages, 4 figures, and 3 tables

References in corpus (40)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Gaia Data Release 3: Summary of the content and survey properties
• The mass distribution and gravitational potential of the Milky Way
• Comprehensive nucleosynthesis analysis for ejecta of compact binary mergers
• Magnetorotationally driven Supernovae as the origin of early galaxy $r$-process elements?
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
• Discovery of HE 1523-0901, a Strongly r-Process Enhanced Metal-Poor Star with Detected Uranium
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability
• Chemical evolution with rotating massive star yields II. A new assessment of the solar s- and r- process components
• APASS Landolt-Sloan BVgri photometry of RAVE stars. I. Data, effective temperatures and reddenings
• Four-hundred Very Metal-Poor Stars Studied with LAMOST and Subaru. II. Elemental abundances
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• linemake: An Atomic and Molecular Line List Generator
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• The Hamburg/ESO R-process Enhanced Star survey (HERES) X. HE 2252-4225, one more r-process enhanced and actinide-boost halo star
• R-Process elements from magnetorotational hypernovae
• High-resolution abundance analysis of very metal-poor r-I stars
• RAVE J203843.2-002333: The first highly r-process-enhanced star identified in the RAVE survey
• Can neutron star mergers alone explain the r-process enrichment of the Milky Way?
• The Parallax Zero-Point of Gaia Early Data Release 3 from LAMOST Primary Red Clump Stars
• Element abundance patterns in stars indicate fission of nuclei heavier than uranium
• The R-Process Alliance: Abundance Universality among Some Elements at and between the First and Second R-Process Peaks
• The R-Process Alliance: J1521-3538, a very metal-poor, extremely r-process-enhanced star with [Eu/Fe]=+2.2, and the class of r-III stars
• R-process-rich stellar streams in the Milky Way
• The R-Process Alliance: Chemo-Dynamically Tagged Groups II. An Extended Sample of Halo $r$-Process-Enhanced Stars
• The R-Process Alliance: Fifth Data Release from the Search for R-Process-Enhanced Metal-poor Stars in the Galactic Halo with the GTC
• Decoding the compositions of four bright $r$-process-enhanced stars
• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
• Uranium Abundances and Ages of $R$-process Enhanced Stars with Novel U II Lines
• Actinide-boosting r Process in Black Hole-Neutron Star Merger Ejecta
• Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th
• Exploring the ex-situ components within Gaia DR3
• A Modified Initial Mass Function of the First Stars with Explodability Theory under Different Enrichment Scenarios
• Discovery of a pair of very metal-poor stars enriched in neutron-capture elements: The proto-disk r-II star BPS CS 29529-0089 and the Gaia-Sausage-Enceladus r-I star TYC 9219-2422-1
• Detection of the actinide Th in an r-process-enhanced star with accretion origin

Cited by in corpus (2)

• Universality and variability of the heavy r-process element abundance pattern from a nonequilibrium approach
• Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars