The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History

Abstract

We derive dynamical parameters for a large sample of 446 $r$-process-enhanced (RPE) metal-poor stars in the halo and disk systems of the Milky Way, based on data releases from the $R$-Process Alliance, supplemented by additional literature samples. This sample represents more than a ten-fold increase in size relative to that previously considered by Roederer et al., and, by design, covers a larger range of $r$-process-element enrichment levels. We test a number of clustering analysis methods on the derived orbital energies and other dynamical parameters for this sample, ultimately deciding on application of the HDBSCAN algorithm, which obtains 30 individual Chemo-Dynamically Tagged Groups (CDTGs); 21 contain between 3 and 5 stars, and 9 contain between 6 and 12 stars. Even though the clustering was performed solely on the basis of their dynamical properties, the stars in these CDTGs exhibit statistically significant similarities in their metallicity ([Fe/H]), carbonicity ([C/Fe]), and neutron-capture element ratios ([Sr/Fe], [Ba/Fe], and [Eu/Fe]). These results demonstrate that the RPE stars in these CDTGs have likely experienced common chemical-evolution histories, presumably in their parent satellite galaxies or globular clusters, prior to being disrupted into the Milky Way's halo. We also confirm the previous claim that the orbits of the RPE stars preferentially exhibit pericentric distances that are substantially lower than the present distances of surviving ultra-faint dwarf and canonical dwarf spheroidal galaxies, consistent with the disruption hypothesis. The derived dynamical parameters for several of our CDTGs indicate their association with previously known substructures, Dynamically Tagged Groups, and RPE Groups.

To be published in the Astrophysical Journal

References in corpus (41)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The Gaia mission
• The mass distribution and gravitational potential of the Milky Way
• The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Magnetorotationally driven Supernovae as the origin of early galaxy $r$-process elements?
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• 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
• Identification of strontium in the merger of two neutron stars
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Neutron Star Mergers and Nucleosynthesis of Heavy Elements
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger
• Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
• Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. I. Spherically symmetric hydrodynamic simulations
• 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
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• Silver and palladium help unveil the nature of a second r-process
• Distances and parallax bias in Gaia DR2
• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• i-process nucleosynthesis and mass retention efficiency in He-shell flash evolution of rapidly accreting white dwarfs
• Elemental abundances and classification of CEMP stars
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• 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
• High-resolution abundance analysis of very metal-poor r-I stars
• Lithium abundances in CEMP stars
• RAVE J203843.2-002333: The first highly r-process-enhanced star identified in the RAVE survey
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• Evidence for the accretion origin of halo stars with an extreme r-process enhancement
• Metal-poor stars observed with the automated planet finder telescope. I. Discovery of five carbon-enhanced metal-poor stars from LAMOST
• The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510
• 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
• Nucleosynthetic Yields from Neutron Stars Accreting in Binary Common Envelopes

Cited by in corpus (10)

• StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream
• Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-Faint Dwarf Galaxies
• Decoding the compositions of four bright $r$-process-enhanced stars
• Dynamics of Stellar Disk Tilting from Satellite Mergers
• Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th
• Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22