Probing the Galactic halo with RR Lyrae stars -- IV. On the Oosterhoff dichotomy of RR Lyrae stars

Abstract

We use 3653 (2661 RRab, 992 RRc) RR Lyrae stars (RRLs) with 7D (3D position, 3D velocity, and metallicity) information selected from SDSS, LAMOST, and Gaia EDR3, and divide the sample into two Oosterhoff groups (Oo I and Oo II) according to their amplitude-period behaviour in the Bailey Diagram. We present a comparative study of these two groups based on chemistry, kinematics, and dynamics. We find that Oo I RRLs are relatively more metal rich, with predominately radially dominated orbits and large eccentricities, while Oo II RRLs are relatively more metal poor, and have mildly radially dominated orbits. The Oosterhoff dichotomy of the Milky Way's halo is more apparent for the inner-halo region than for the outer-halo region. Additionally, we also search for this phenomenon in the halos of the two largest satellite galaxies, the Large and Small Magellanic clouds (LMC, SMC), and compare over different bins in metallicity. We find that the Oosterhoff dichotomy is not immutable, and varies based on position in the Galaxy and from galaxy-to-galaxy. We conclude that the Oosterhoff dichotomy is the result of a combination of stellar and galactic evolution, and that it is much more complex than the dichotomy originally identified in Galactic globular clusters.

References in corpus (52)

• The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• Co-formation of the Galactic disc and the stellar halo
• LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) The survey science plan
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Catalina Surveys Periodic Variable Star Catalog
• The ASAS-SN Catalog of Variable Stars I: The Serendipitous Survey
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• Probing the Outer Galactic halo with RR Lyrae from the Catalina Surveys
• Light Curve Templates and Galactic Distribution of RR Lyrae Stars from Sloan Digital Sky Survey Stripe 82
• The Sausage Globular Clusters
• The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• Tracing the formation of the Milky Way through ultra metal-poor stars
• The SkyMapper-Gaia RVS view of the Gaia-Enceladus-Sausage -- an investigation of the metallicity and mass of the Milky Way's last major merger
• The Milky Way Halo in Action Space
• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• Weak Galactic halo--dwarf spheroidal connection from RR Lyrae stars
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• Determination of the Local Standard of Rest using the LSS-GAC DR1
• RR Lyrae Stars in NGC 6388 and NGC 6441: A New Oosterhoff Group?
• The Circular Velocity Curve of the Milky Way from 5 to 25 kpc using luminous red giant branch star
• The RR Lyrae Period-Amplitude Relation as a Clue to the Origin of the Oosterhoff Dichotomy
• Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$
• On the use of field RR Lyrae as Galactic probes: I. The Oosterhoff dichotomy based on fundamental variables
• Photometric metallicity and distance estimates for $\sim$ 136,000 RR Lyrae stars from Gaia DR3
• RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation
• An In-Depth Spectroscopic Analysis of the Blazhko Star RR Lyr. I. Characterisation of the star: abundance analysis and fundamental parameters
• A "Light," Centrally-Concentrated Milky Way Halo?
• Unmixing the Galactic Halo with RR Lyrae tagging
• High-precision distance measurements with classical pulsating stars
• Probing the galactic halo with RR Lyrae stars I: The catalog
• The QUEST RR Lyrae Survey: III. The Low Galactic Latitude Catalogue
• Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
• The Magellanic System: the puzzle of the leading gas stream
• On the use of field RR Lyrae as Galactic probes: IV. New insights into and around the Oosterhoff dichotomy
• Probing the Galactic Halo with RR Lyrae Stars. II. The Substructures of the Milky Way
• Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter for Stellar Halos
• Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• An Oosterhoff Analysis of the Galactic Bulge Field RR Lyrae stars: Implications On Their Absolute Magnitudes
• On the Metamorphosis of the Bailey diagram for RR Lyrae stars
• Reliability of the measured velocity anisotropy of the Milky Way stellar halo
• Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441
• Asteroseismology of RRab variable star EZ Cnc from K2 photometry and LAMOST spectroscopy
• Lessons from the Magellanic System and its modeling
• Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo
• Field and cluster RR Lyrae stars as stellar tracers

Cited by in corpus (2)

• Photometric-Metallicity and Distance Estimates for $\sim$70,000 RR Lyrae Stars from the Zwicky Transient Facility
• Reconsidering The Bailey Diagrams of ab-type RR Lyrae Stars, Metallicity-Mediated Evolution as the Direct Cause of the Oosterhoff Phenomenon