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.

arXiv commentTo be published in the Astrophysical Journal

References in corpus (121)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Gaia Data Release 2: The astrometric solution
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
• The mass distribution and gravitational potential of the Milky Way
• Co-formation of the Galactic disc and the stellar halo
• 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
• The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• Neutron-Capture Elements in the Early Galaxy: Insights from a Large Sample of Metal-Poor Giants
• AGAMA: Action-based galaxy modelling architecture
• 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
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Hamburg/ESO R-process Enhanced Star survey (HERES) II. Spectroscopic analysis of the survey sample
• Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis
• 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
• The extreme r-element rich, iron-poor halo giant CS31082-001: Implications for the r-process site(s) and radioactive cosmochronology
• R-process enrichment from a single event in an ancient dwarf galaxy
• The early star generations: the dominant effect of rotation on the CNO yields
• Collapsars as a major source of r-process elements
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Spectroscopic Studies of Extremly Metal-Poor Stars with Subaru/HDS:II.The r-process Elements, Including Thorium
• Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way
• Neutron Star Mergers and Nucleosynthesis of Heavy Elements
• Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger
• The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\circ 3248
• The r-process nucleosynthesis in the various jet-like explosions of magnetorotational core-collapse supernovae
• 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
• The r-Process Enriched Low Metallicity Giant HD 115444
• Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger
• Actions for axisymmetric potentials
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
• Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars
• StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars
• First stars XII. Abundances in extremely metal-poor turnoff stars,and comparison with the giants
• Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. I. Spherically symmetric hydrodynamic simulations
• Mapping the substructure in the Galactic halo with the next generation of astrometric satellites
• HE0107-5240, A Chemically Ancient Star.I. A Detailed Abundance Analysis
• Normal and Outlying Populations of the Milky Way Stellar Halo at [Fe/H] < -2
• 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
• Spectroscopic Studies of Very Metal-Poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements
• 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
• From Nuclei to the Cosmos: Tracing Heavy-Element Production with the Oldest Stars
• The r-process in proto-neutron-star wind revisited
• The Ubiquity of the Rapid Neutron-Capture Process
• One large blob and many streams frosting the nearby stellar halo in Gaia DR2
• Tuning the Clock: Uranium and Thorium Chronometers Applied to CS 31082-001
• From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys
• Chemical abundances of the Milky Way thick disk and stellar halo II.: sodium, iron-peak and neutron-capture elements
• Neutron Star Mergers as sites of r-process Nucleosynthesis and Short Gamma-Ray Bursts
• r-Process Nucleosynthesis: Connecting Rare-Isotope Beam Facilities with the Cosmos
• The $R$-Process Alliance: First Release from the Southern Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• 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
• Gaia Proper Motions and Orbits of the Ultra-Faint Milky Way Satellites
• The R-Process Alliance: First Release from the Northern Search for r-Process Enhanced Metal-Poor Stars in the Galactic Halo
• Gaia Data Release 2: Processing the spectroscopic data
• Dynamical Relics of the Ancient Galactic Halo
• JINAbase: A database for chemical abundances of metal-poor stars
• s-Process in Low Metallicity Stars. I. Theoretical Predictions
• Characterization and history of the Helmi streams with Gaia DR2
• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Tracing the formation of the Milky Way through ultra metal-poor stars
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The Near Infrared Ca II Triplet as Metallicity Indicator: II Extension to extremely metal-poor metallicity regimes
• 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
• The EMBLA Survey -- Metal-poor stars in the Galactic bulge
• 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 Chemical Abundances of Stars in the Halo (CASH) Project. II. A Sample of 16 Extremely Metal-poor Stars
• The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
• 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
• The r-process in the early Galaxy
• Elemental abundances and classification of CEMP stars
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• Neutron-Capture Nucleosynthesis in the First Stars
• Non standard s-process in massive rotating stars. Yields of $10-150$ $M_{\odot }$ models at $Z=10^{-3}$
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• The R-Process Alliance: 2MASS J09544277+5246414, the Most Actinide-Enhanced R-II Star Known
• Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites
• Actinide Production in Neutron-Rich Ejecta of a Neutron Star Merger
• 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
• Extreme Enhancements of r-process Elements in the Cool Metal-Poor Main-Sequence Star SDSS J2357-0052
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• StarGO: A New Method to Identify the Galactic Origins of Halo Stars
• Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis
• High-resolution spectroscopic studies of ultra metal-poor stars found in LAMOST survey
• Actinide-rich and Actinide-poor $r$-Process Enhanced Metal-Poor Stars do not Require Separate $r$-Process Progenitors
• Evidence for the Third Stellar Population in the Milky Way's Disk
• The Origin of r-process Enhanced Metal-Poor Halo Stars In Now-Destroyed Ultra-Faint Dwarf Galaxies
• The INT Search for Metal-Poor Stars. Spectroscopic Observations and Classification via Artificial Neural Networks
• The Fastest Travel Together: Chemical Tagging of the Fastest Stars in Gaia DR2 to the Stellar Halo
• A Blueprint for the Milky Way's Stellar Populations: The Power of Large Photometric and Astrometric Surveys
• Evidence for the accretion origin of halo stars with an extreme r-process enhancement
• The S2 Stream: the shreds of a primitive dwarf galaxy
• 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
• The R-Process Alliance: Chemical Abundances for a Trio of R-Process-Enhanced Stars -- One Strong, One Moderate, One Mild
• The Tilt of the Local Velocity Ellipsoid as Seen by Gaia
• Metal-Poor Stars Observed with the Southern African Large Telescope
• Nucleosynthetic Yields from Neutron Stars Accreting in Binary Common Envelopes

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• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• 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
• Element abundance patterns in stars indicate fission of nuclei heavier than uranium
• The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO
• Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way
• Origin of highly $r$-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
• 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
• Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream
• The R-Process Alliance: Chemo-Dynamically Tagged Groups II. An Extended Sample of Halo $r$-Process-Enhanced Stars
• Dynamically Tagged Groups of Metal-Poor Stars II. The Radial Velocity Experiment Data Release 6
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
• Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-Faint Dwarf Galaxies
• Decoding the compositions of four bright $r$-process-enhanced stars
• $S^5$: The destruction of a bright dwarf galaxy as revealed by the chemistry of the Indus stellar stream
• NGC 1261: an $r$-process enhanced globular cluster from the Gaia-Enceladus event
• Dynamics of Stellar Disk Tilting from Satellite Mergers
• Using Action Space Clustering to Constrain the Accretion History of Milky Way like Galaxies
• Finding $r$-II sibling stars in the Milky Way with the Greedy Optimistic Clustering algorithm
• Robust Clustering of the Local Milky Way Stellar Kinematic Substructures with Gaia eDR3
• Metal-Poor Stars Observed with the Southern African Large Telescope II. An Extended Sample
• The S-PLUS Ultra-Short Survey: first data release
• Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th
• A chemodynamical analysis of bright metal-poor stars from the HESP-GOMPA survey -- Indications of a non-prevailing site for light r-process elements
• 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
• Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22
• Revealing the Milky Way's Most Recent Major Merger with a Gaia EDR3 Catalog of Machine-Learned Line-of-Sight Velocities
• The neutron-capture and alpha-elements abundance ratios scatter in old stellar populations. Cosmological simulations of the stellar halo
• Recent Advances in Understanding R-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems
• The R-Process Alliance: Hunting for gold in the near-UV spectrum of 2MASS J05383296-5904280
• The R-Process Alliance: Exploring the cosmic scatter among ten r-process sites with stellar abundances
• Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample
• Two faces of Gaia-Sausage-Enceladus: Mining the chemical abundance space with graph attention networks
• The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925