Chemo-dynamics of outer halo dwarf stars, including \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia candidates

Abstract

The low-metallicity, kinematically interesting dwarf stars studied by Stephens \& Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H]$>-2$; however, large disagreements are found for stars with [Fe/H]$\le -2$, with offsets as large as $\Delta$T${}_{\mathrm{eff}}\sim +500$ K and $\Delta$log\,$g\sim +1.0$. A subset of six stars (test cases) are analysed ab initio using high resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two $\alpha$-challenged dwarf stars, suggestive of origins in a low mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using \textit{Gaia} DR2 data. We find 11 stars that are dynamically coincident with the \textit{Gaia}-Sausage accretion event and another 17 with the \textit{Gaia}-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within \textit{Gaia}-Sequoia. When these subsets are examined separately, a common knee in [$\alpha$/Fe] is found for the \textit{Gaia}-Sausage and low orbital energy \textit{Gaia}-Sequoia stars. A lower metallicity knee is tentatively identified in the \textit{Gaia}-Sequoia high orbital energy stars. If the metal-poor dwarf stars in these samples are true members of the \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia events, then they present a unique opportunity to probe the earlier, more pristine, star formation histories of these systems.

arXiv comment20-21 pages, 20 figures, accepted for publication in MNRAS Slight mismatch between published version and arXiv version, rectified now

References in corpus (90)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The chemical composition of the Sun
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The USNO-B Catalog
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Local Kinematics and the Local Standard of Rest
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The Dartmouth Stellar Evolution Database
• galpy: A Python Library for Galactic Dynamics
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• The mass distribution and gravitational potential of the Milky Way
• Co-formation of the Galactic disc and the stellar halo
• The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment
• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• The Proper Motion of Sgr A*: II. The Mass of Sgr A*
• Stellar Chemical Signatures And Hierarchical Galaxy Formation
• Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Non-Kinematically Selected Stars
• Gaia Data Release 2: Catalogue validation
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
• Gaia Data Release 2: first stellar parameters from Apsis
• Vertical waves in the solar neighbourhood in Gaia DR2
• The Circular Velocity Curve of the Milky Way from $5$ to $25$ kpc
• Gaia Data Release 1: Catalogue validation
• In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
• NLTE line formation of Fe for late-type stars. I. Standard stars with 1D and <3D> model atmospheres
• NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters
• The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
• On the use of Gaia magnitudes and new tables of bolometric corrections
• Actions for axisymmetric potentials
• The birth of the Milky Way as uncovered by accurate stellar ages with Gaia
• VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies: II. Implications for Understanding Galaxy Evolution
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
• A high resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy
• The Milky Way has no in-situ halo other than the heated thick disc. Composition of the stellar halo and age-dating the last significant merger with Gaia DR2 and APOGEE
• Using chemical tagging to redefine the interface of the Galactic disk and halo
• The Sausage Globular Clusters
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Chemistry of the Sagittarius Dwarf Galaxy: a Top-Light IMF, Outflows and the R-Process
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
• Reappraising the Spite Lithium Plateau: Extremely Thin and Marginally Consistent with WMAP
• Nucleosynthesis and the Inhomogeneous Chemical Evolution of the Carina Dwarf Galaxy
• Abundances and Kinematics of Field Stars II: Kinematics and Abundance Relationships
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• Dynamical Relics of the Ancient Galactic Halo
• An R-process enhanced star in the dwarf galaxy Tucana III
• The Bizarre Chemical Inventory of NGC 2419, An Extreme Outer Halo Globular Cluster
• VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy
• Tracing the formation of the Milky Way through ultra metal-poor stars
• The Milky Way Halo in Action Space
• Origin of the excess of high-energy retrograde stars in the Galactic halo
• Chemical Abundances in the Ultra-Faint Dwarf Galaxies Grus I and Triangulum II: Neutron-Capture Elements as a Defining Feature of the Faintest Dwarfs
• Metal Abundances and Kinematics of Bright Metal-Poor Giants Selected from the LSE Survey: Implications for the Metal-Weak Thick Disk
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
• Not All Stars Are the Sun: Empirical Calibration of the Mixing Length for Metal-Poor Stars Using One-dimensional Stellar Evolution Models
• Fast estimation of orbital parameters in Milky-Way-like potentials
• In the thick of it: metal-poor disc stars in RAVE
• The early days of the Sculptor dwarf spheroidal galaxy
• What determines galactic evolution?
• Benchmark stars for Gaia: fundamental properties of the Population II star HD140283 from interferometric, spectroscopic and photometric data
• Disentangling the Galactic Halo with APOGEE: II. Chemical and Star Formation Histories for the Two Distinct Populations
• Pristine IX: CFHT ESPaDOnS Spectroscopic Analysis of 115 Bright Metal-Poor Candidate Stars
• The Stagger-grid: A grid of 3D stellar atmosphere models V. Synthetic stellar spectra and broad-band photometry
• Manganese in dwarf spheroidal galaxies
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Manganese Indicates a Transition from Sub- to Near-Chandrasekhar Type Ia Supernovae in Dwarf Galaxies
• Zinc in the Sculptor dwarf spheroidal galaxy
• The Populations of Carina. II. Chemical Enrichment
• Unmixing the Galactic Halo with RR Lyrae tagging
• The age structure of the Milky Way's halo
• Deep SDSS optical spectroscopy of distant halo stars II. Iron, calcium, and magnesium abundances
• Gemini/GRACES Spectroscopy of Stars in Triangulum II
• Through Thick and Thin: Kinematic and Chemical Components in the Solar Neighbourhood
• Atomic transition probabilities for UV and blue lines of Fe II and abundance determinations in the photospheres of the Sun and metal-poor star HD 84937
• Chemical trends in the Galactic Halo with APOGEE data
• Neutron-capture elements in dwarf galaxies II: Challenges for the s- and i-processes at low metallicity
• Detailed Iron-Peak Element Abundances in Three Very Metal-Poor Stars
• Investigating the Consistency of Stellar Evolution Models with Globular Cluster Observations via the Red Giant Branch Bump
• Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process
• What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants

Cited by in corpus (51)

• The GALAH+ Survey: Third Data Release
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• The chemical characterisation of halo substructure in the Milky Way based on APOGEE
• Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Reconstructing the Disrupted Dwarf Galaxy $Gaia$-Sausage/Enceladus Using its Stars and Globular Clusters
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• Galactic Archaeology with Gaia
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• Exploring the origin of low-metallicity stars in Milky Way-like galaxies with the NIHAO-UHD simulations
• Pristine IX: CFHT ESPaDOnS Spectroscopic Analysis of 115 Bright Metal-Poor Candidate Stars
• Exploring the Galaxy's halo and very metal-weak thick disk with SkyMapper and Gaia DR2
• The Kinematic Properties of Milky Way Stellar Halo Populations
• Substructure in the stellar halo near the Sun. II. Characterisation of independent structures
• High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia
• The Pristine survey -- XII: Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy
• Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
• Metallicity Distribution Functions of 13 Ultra-Faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• The Pristine Inner Galaxy Survey (PIGS) V: a chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge
• Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream
• 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
• Metallicity distributions of halo stars: do they trace the Galactic accretion history?
• Dynamically Tagged Groups of Metal-Poor Stars II. The Radial Velocity Experiment Data Release 6
• The observable properties of galaxy accretion events in Milky Way-like galaxies in the FIRE-2 cosmological simulations
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
• Assessing the performance of LTE and NLTE synthetic stellar spectra in a machine learning framework
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• The GALAH Survey: Accreted stars also inhabit the Spite Plateau
• Extending the Chemical Reach of the H3 Survey: Detailed Abundances of the Dwarf-galaxy Stellar Stream Wukong/LMS-1
• Photometric metallicity for 694233 Galactic giant stars from Gaia DR3 synthetic Stromgren photometry. Metallicity distribution functions of halo sub-structures
• Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. III. Dynamically Tagged Groups and Chemodynamical Properties
• Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
• NGC 1261: an $r$-process enhanced globular cluster from the Gaia-Enceladus event
• Exploring the chemodynamics of metal-poor stellar populations
• High Velocity Stars in SDSS/APOGEE DR17
• A high fidelity Milky Way simulation with Kraken, Gaia-Enceladus, and Sequoia analogues: clues to their accretion histories
• Chemo-dynamics and asteroseismic ages of seven metal-poor red giants from the Kepler field
• G112-43/44: A metal-poor binary star with a unique chemical composition and kinematics like the Helmi streams
• Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362
• The global structure of the Milky Way's stellar halo based on the orbits of local metal-poor stars
• Chemodynamics of metal-poor wide binaries in the Galactic halo: Association with the Sequoia event
• Magnesium isotope ratios in Milky Way and dwarf galaxy stars
• Combining Astrometry and Elemental Abundances: The Case of the Candidate Pre-Gaia Halo Moving Groups G03-37, G18-39, and G21-22
• The R-Process Alliance: Exploring the cosmic scatter among ten r-process sites with stellar abundances
• The metal-poorest tail of the Galactic halo: hypothesis on its origin from precise spectral analysis
• Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample
• HR-GO II: chemical abundances of low-$E$ retrograde dynamically-tagged-groups: Revealing Thamnos as a very metal-poor substructure
• Probing the Milky Way Halo with RR Lyrae Stars from Gaia Data Release 3