RR Lyrae stars as probes of the outer Galactic halo: Chemical and kinematic analysis of a pilot sample

Abstract

We report the spectroscopic analysis of 20 halo ab-type RR Lyrae stars with heliocentric distances between 15 and 165 kpc, conducted using medium-resolution spectra from the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We obtain the systemic line-of-sight velocities of our targets with typical uncertainties of 5-10 km s${}^{-1}$, and compute orbital parameters for a subsample out to 50 kpc from the Galactic centre, including proper motion data from Gaia DR3. The orientation of our stars' orbits, determined for an isolated Milky Way and for a model perturbed by the Large Magellanic Cloud, appears to suggest an accreted origin for at least half of the sample. In addition, we derive atmospheric parameters and chemical abundance ratios for seven stars beyond 20 kpc. The derived $\alpha$-abundances of five of these stars follow a Milky Way halo-like trend, while the other two display an underabundance of $\alpha$-elements for their [Fe/H], indicating an association with accretion events. Furthermore, based on the [Sr/Ba] ratio, we can speculate about the conditions for the formation of a potential chemically peculiar carbon-enhanced metal-poor (CEMP) RR Lyrae star. By analysing the stars' orbital parameters and abundance ratios, we find hints of association of two of our stars with two massive satellites, namely the Large Magellanic Cloud and Sagittarius. Overall, our results are in line with the suggestion that the accretion of sub-haloes largely contributes to the outer halo stellar populations.

arXiv comment33 pages, 22 figures, 7 tables. Published in MNRAS. Accepted 2022 December 2. Received 2022 November 30; in original form 2022 August 1

References in corpus (174)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The chemical composition of the Sun
• 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
• galpy: A Python Library for Galactic Dynamics
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• The New Galaxy: Signatures of its Formation
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• The Dark Energy Camera
• Tracing Galaxy Formation with Stellar Halos I: Methods
• The Dark Energy Survey: more than dark energy - an overview
• Co-formation of the Galactic disc and the stellar halo
• The Pan-STARRS1 Photometric System
• New catalogue of optically visible open clusters and candidates
• A Recipe for Galaxy Formation Shaun Cole
• The s Process: Nuclear Physics, Stellar Models, Observations
• Stellar Chemical Signatures And Hierarchical Galaxy Formation
• An absolutely calibrated effective temperature scale from the InfraRed Flux Method
• Origin of the Heaviest Elements: the Rapid Neutron-Capture Process
• Extragalactic Science, Cosmology and Galactic Archaeology with the Subaru Prime Focus Spectrograph (PFS)
• A distance to the Large Magellanic Cloud that is precise to one per cent
• Optimal Techniques in Two-dimensional Spectroscopy: Background Subtraction for the 21st Century
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• New Understanding of Large Magellanic Cloud Structure, Dynamics and Orbit from Carbon Star Kinematics
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars
• The Catalina Surveys Periodic Variable Star Catalog
• On the use of empirical bolometric corrections for stars
• Origin of the system of globular clusters in the Milky Way
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• The formation and assembly history of the Milky Way revealed by its globular cluster population
• 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
• The Masses of the Milky Way and Andromeda galaxies
• The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• Modern stellar spectroscopy caveats
• Gaia FGK Benchmark Stars - Metallicity
• The Zwicky Transient Facility Catalog of Periodic Variable Stars
• Tango for three: Sagittarius, LMC, and the Milky Way
• Stellar Streams Discovered in the Dark Energy Survey
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• Third-Epoch Magellanic Cloud Proper Motions II: The Large Magellanic Cloud Rotation Field in Three Dimensions
• Periodograms for Multiband Astronomical Time Series
• The SAGA Survey: I. Satellite Galaxy Populations Around Eight Milky Way Analogs
• Detection of a 60 Degree-Long Dwarf Galaxy Debris Stream
• $s$-process production in rotating massive stars at solar and low metallicities
• Lambda-Cold Dark Matter, Stellar Feedback, and the Galactic Halo Abundance Pattern
• The Evolution of Early-Type Galaxies in Distant Clusters II: Internal Kinematics of 55 Galaxies in the z=0.33 Cluster CL1358+62
• Observational constraints on the origin of the elements. IV: The standard composition of the Sun
• Light Curve Templates and Galactic Distribution of RR Lyrae Stars from Sloan Digital Sky Survey Stripe 82
• Gaia reveals a metal-rich in-situ component of the local stellar halo
• A non-LTE study of neutral and singly-ionized calcium in late-type stars
• The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
• Ghostly Tributaries to the Milky Way: Charting the Halo's Stellar Streams with the Gaia DR2 catalogue
• From the bulge to the outer disc: StarHorse stellar parameters, distances, and extinctions for stars in APOGEE DR16 and other spectroscopic surveys
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• Charting the Galactic acceleration field I. A search for stellar streams with Gaia DR2 and EDR3 with follow-up from ESPaDOnS and UVES
• The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
• Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation
• Silver and palladium help unveil the nature of a second r-process
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: Variation of the Metallicity Distribution Function Along the Sagittarius Stream
• APOGEE Chemical Abundance Patterns of the Massive Milky Way Satellites
• The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets
• Metal Abundances, Radial Velocities and other Physical Characteristics for the RR Lyrae Stars in the Kepler Field
• The total stellar halo mass of the Milky Way
• Response of the Milky Way's disc to the Large Magellanic Cloud in a first infall scenario
• The Gaia FGK Benchmark Stars - High resolution spectral library
• Ionization balance of Ti in the photospheres of the Sun and four late-type stars
• Galactic Stellar Populations in the Era of SDSS and Other Large Surveys
• Phase-Space Distributions of Chemical Abundances in Milky Way-type Galaxy Halos
• The mass of our Milky Way
• Piercing the Milky Way: an all-sky view of the Orphan Stream
• The composition of HB stars : RR Lyrae variables
• The GALAH survey: An abundance, age, and kinematic inventory of the solar neighbourhood made with TGAS
• STREAMFINDER I: A New Algorithm for detecting Stellar Streams
• A Synoptic Map of Halo Substructures from the Pan-STARRS1 3π Survey
• Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by $S^5$
• Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey
• Limit on the LMC mass from a census of its satellites
• Non-local thermodynamic equilibrium stellar spectroscopy with 1D and <3D> models - I. Methods and application to magnesium abundances in standard stars
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• The Konkoly Blazhko Survey: Is light-curve modulation a common property of RRab stars?
• On the Blazhko Effect in RR Lyrae Stars
• Before the Bar: Kinematic Detection of A Spheroidal Metal-Poor Bulge Component
• Kinematics of Antlia 2 and Crater 2 from The Southern Stellar Stream Spectroscopic Survey (S5)
• The Chemical Compositions of Variable Field Horizontal Branch Stars: RR Lyrae Stars
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• A Low-Mass Stellar-Debris Stream Associated with a Globular Cluster Pair in the Halo
• Old-Aged Stellar Population Distance Indicators
• Non standard s-process in massive rotating stars. Yields of $10-150$ $M_{\odot }$ models at $Z=10^{-3}$
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• Revealing Substructure in the Galactic Halo - The SEKBO RR Lyrae Survey
• Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed with the Kepler space telescope
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites
• Fourteen candidate RR Lyrae star streams in the inner Galaxy
• The mass of the Milky Way out to 100 kpc using halo stars
• Whiting 1: the youngest globular cluster associated with the Sgr dSph
• The formation of the Milky Way halo and its dwarf satellites, a NLTE-1D abundance analysis. I. Homogeneous set of atmospheric parameters
• A tale of two populations: surviving and destroyed dwarf galaxies and the build up of the Milky Way's stellar halo
• Metallicity and $\alpha$-element Abundance Gradients along the Sagittarius Stream as Seen by APOGEE
• Spectroscopic Comparison of Metal-Rich RRab Stars of the Galactic Field with Their Metal-Poor Counterparts
• La Silla QUEST RR Lyrae Star Survey: Region I
• Fourier decomposition and frequency analysis of the pulsating stars with P < 1day in the OGLE database. II. Multiperiodic RR Lyrae variables in the Galactic Bulge
• Long time-scale behavior of the Blazhko effect from rectified Kepler data
• Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream
• Modelling the Tucana III stream - a close passage with the LMC
• Ages and heavy element abundances from very metal-poor stars in the Sagittarius dwarf galaxy
• The eye of Gaia on globular clusters structure: tidal tails
• Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• A stellar stream remnant of a globular cluster below the metallicity floor
• Bayesian Mass Estimates of the Milky Way II: The dark and light sides of parameter assumptions
• On the Use of Field RR Lyrae as Galactic Probes. II. A new $\Delta$S calibration to estimate their metallicity
• First stars XIII. Two extremely metal-poor RR Lyrae stars?
• A comparison of the s- and r-process element evolution in local dwarf spheroidal galaxies and in the Milky Way
• Search for RR Lyrae stars in DES ultra-faint systems: Grus I, Kim 2, Phoenix II, and Grus II
• The High Cadence Transient Survey (HiTS) - I. Survey design and supernova shock breakout constraints
• Chemical abundances of hydrostatic and explosive alpha-elements in Sagittarius stream stars
• Chemical abundances of solar neighborhood RR Lyrae stars
• The metallicity distribution of the halo and the satellites of the Milky way in the hierarchical merging paradigm
• The RRC Stars: Chemical Abundances and Envelope Kinematics
• Facing the problems on the determination of stellar temperatures and gravities: Galactic globular clusters
• Template RR Lyrae H alpha, H beta, and H gamma Velocity Curves
• The r-Process Pattern of a Bright, Highly r-Process-Enhanced, Metal-Poor Halo Star at [Fe/H] ~ -2
• An In-Depth Spectroscopic Analysis of the Blazhko Star RR Lyr. I. Characterisation of the star: abundance analysis and fundamental parameters
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• Unmixing the Galactic Halo with RR Lyrae tagging
• Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers
• Identifying Sagittarius Stream Stars By Their APOGEE Chemical Abundance Signatures
• The Pristine survey -- XVI. The metallicity of 26 stellar streams around the Milky Way detected with the STREAMFINDER in Gaia EDR3
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: I. Period-Fourier-Metallicity Relations for Fundamental Mode RR Lyrae
• Whiting 1: a new Halo Young Globular Cluster
• Probing the galactic halo with RR Lyrae stars I: The catalog
• The shortest modulation period Blazhko RR Lyrae star: SS Cnc
• Metallicity distribution functions of the old populations of the Magellanic Clouds from RR Lyrae stars
• On the Use of Field RR Lyrae as Galactic Probes. III. The $\alpha$-element abundances
• The ISLAnds Project III: Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies
• Explaining the Sr and Ba Scatter in Extremely Metal-Poor Stars
• The Southern Dwarf Hunt: Local Group Dwarf Candidates in the Southern Sky
• Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey
• A Data-driven Study of RR Lyrae Near-IR Light Curves: Principal Component Analysis, Robust Fits, and Metallicity Estimates
• A Near-infrared RR Lyrae census along the southern Galactic plane: the Milky Way's stellar fossil brought to light
• On the use of field RR Lyrae as Galactic probes: IV. New insights into and around the Oosterhoff dichotomy
• New LZ and PW(Z) relations of RR Lyrae stars calibrated with Gaia EDR3 parallaxes
• Revealing the Structure and Internal Rotation of the Sagittarius Dwarf Spheroidal Galaxy with Gaia and Machine Learning
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• Chemical Compositions of Field and Globular Cluster RR Lyrae Stars: I. NGC 3201
• Radial Velocities and Pulsation Ephemerides of 11 Field RR Lyrae Stars
• Metallicities from high resolution spectra of 49 RR Lyrae Variables
• Chemical Compositions of Field and Globular Cluster RR~Lyrae Stars: II. omega Centauri
• Stellar atmosphere parameters with MAx, a MAssive compression of x^2 for spectral fitting
• At a Crossroads: Stellar Streams in the South Galactic Cap
• The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo
• Chemical abundances in a high velocity RR Lyrae star near the bulge
• On the Oosterhoff dichotomy in the Galactic bulge: I. spatial distribution
• Milky Way archaeology using RR Lyrae and type II Cepheids I. The Orphan stream in 7D using RR Lyrae stars
• Metallicity and Kinematics of the Galactic halo from the LAMOST sample stars
• Chemical abundances of metal-poor RR Lyrae stars in the Magellanic Clouds
• New views of the distant stellar halo
• Metallicity of Galactic RR Lyrae from Optical and Infrared Light Curves: II. Period-Fourier-Metallicity Relations for First Overtone RR Lyrae
• Metal Abundance Calibration of the Ca II Triplet Lines in RR Lyrae Stars
• Seven New Carbon-Enhanced Metal-Poor RR Lyrae Stars
• A high-precision abundance analysis of the nuclear benchmark star HD 20
• Tails from the Orphanage
• Identifying RR Lyrae in the ZTF DR3 dataset
• An empirical metallicity tracer in CEMP and C-normal stars

Cited by in corpus (2)

• On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid
• High-cadence stellar variability studies of RR Lyrae stars with DECam: New multi-band templates