On the Oosterhoff dichotomy in the Galactic bulge: II. kinematical distribution

Abstract

We present a kinematical study of RR~Lyrae stars associated with two Oosterhoff groups in the Galactic bulge. We used data published in the first paper of the series, plus proper motions from the {\it Gaia} Data Release 2, and radial velocities from the literature. A 6D kinematical and spatial solution was obtained for 429 RR~Lyrae stars. We use a model of the Galactic gravitational potential to infer stellar orbits. We did not find a difference between the Oosterhoff groups in the individual components of the space velocity. We report that \textit{foreground} and \textit{background} stars with respect to the Galactic bulge stand out in the mean $V$ velocity component, which we interpret as a sign of the Galactic rotation. The movement of the studied stars in the central region of the Galactic bulge is consistent with random motions expected for a classical bulge component. From the orbital integration, we estimate that 8\,\% of the RR~Lyrae stars are halo interlopers currently located in the Galactic bulge. The majority of the stars' orbits are within a 3\,kpc radius from the Galactic bulge. The fraction of Oosterhoff\,II stars increases with increasing Galactic latitude, as well as towards longer orbital periods. We found several RR~Lyrae stars with high space velocities, one of which has an extremely long orbital period of $\sim$1\,Gyr. We conclude that based on their kinematics, the vast majority of the stars in our sample do not seem to contribute to the boxy/peanut component of the Galactic bulge.

arXiv comment11 pages, 8 figures, Accepted for publication in MNRAS

References in corpus (43)

• A Universal Density Profile from Hierarchical Clustering
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Local Kinematics and the Local Standard of Rest
• Monitoring stellar orbits around the Massive Black Hole in the Galactic Center
• Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• galpy: A Python Library for Galactic Dynamics
• VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• The Effect of the Outer Lindblad Resonance of the Galactic Bar on the Local Stellar Velocity Distribution
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars
• The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• ARGOS III: Stellar Populations in the Galactic Bulge of the Milky Way
• Two Red Clumps and the X-Shaped Milky Way Bulge
• Galactic Rotation and Solar Motion from Stellar Kinematics
• Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2
• Probing the Outer Galactic halo with RR Lyrae from the Catalina Surveys
• The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data Release
• Chemodynamical history of the Galactic Bulge
• ARGOS IV: The Kinematics of the Milky Way Bulge
• Galactic Bulges
• Deciphering the 3D structure of the old Galactic bulge from the OGLE RR Lyrae stars
• The Shape and Profile of the Milky Way Halo as Seen by the CFHT Legacy Survey
• The Absolute Magnitude and Kinematics of RR Lyrae Stars via Statistical Parallax
• VVV Survey Near-Infrared Photometry of Known Bulge RR Lyrae stars: the Distance to the Galactic Center and Absence of a Barred Distribution of the Metal-Poor Population
• ARGOS II: The Galactic Bulge Survey
• Exploring the Variable Sky with LINEAR. II. Halo Structure and Substructure Traced by RR Lyrae Stars to 30 kpc
• Before the Bar: Kinematic Detection of A Spheroidal Metal-Poor Bulge Component
• RR Lyrae Stars in NGC 6388 and NGC 6441: A New Oosterhoff Group?
• The complex case of V445 Lyr observed with Kepler: Two Blazhko modulations, a non-radial mode, possible triple mode RR Lyrae pulsation, and more
• A two-phase scenario for bulge assembly in LCDM cosmologies
• MACHO Project Photometry of RR Lyrae Stars in the Sgr Dwarf Galaxy
• Metal abundances of RR Lyrae stars in the metal rich globular cluster NGC 6441
• Blazhko effect in the Galactic bulge fundamental mode RR~Lyrae stars I: Incidence rate and differences between modulated and non-modulated stars
• A Near-infrared RR Lyrae census along the southern Galactic plane: the Milky Way's stellar fossil brought to light
• A high-velocity bulge RR Lyrae variable on a halo-like orbit
• Structure and kinematics of Type II Cepheids in the Galactic bulge based on near-infrared VVV data
• Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection. I. Long-period stars with dominant radial fundamental mode
• Chemical abundances in a high velocity RR Lyrae star near the bulge
• Radial velocities of RR Lyrae stars in and around NGC 6441

Cited by in corpus (9)

• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• Evidence for Galactic disc RR~Lyrae stars in the Solar neighbourhood
• Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results
• Milky Way archaeology using RR Lyrae and type II Cepheids II. High velocity RR Lyrae stars, and mass of the Milky Way
• Near-Infrared Search for Fundamental-mode RR Lyrae Stars Toward the Inner Bulge by Deep Learning
• Comparing bulge RR Lyrae stars with bulge giants -- Insight from 3D kinematics
• The Galactic Bulge exploration IV.: RR~Lyrae stars as traces of the Galactic bar -- 3D and 5D analysis, extinction variation
• RRab variables with identical light-curve shapes at different pulsation periods
• RR Lyrae stars with variable mean magnitudes