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 (17)

• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Catalina Surveys Periodic Variable Star Catalog
• 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 Galactic globular clusters. VI. The Period-Amplitude relation
• High-precision distance measurements with classical pulsating stars
• 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
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• On the Metamorphosis of the Bailey diagram for RR Lyrae stars
• 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