A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

Abstract

Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions from multiple sources have been averaged to produce a significant improvement in the transverse space velocity errors. In most cases, this exceeds the accuracy of Hipparcos proper motions alone. The velocity ellipsoids computed for halo and thick disk samples are in agreement with previous studies. No distinct sample of thin disk RR Lyraes has been isolated but there is kinematic evidence for some thin disk stars in our thick disk samples. A sample of 21 stars with [Fe/H] < -1.0 and disk-like kinematics have been isolated. It is concluded from their kinematics and spatial distribution that these stars represent a sample of RR Lyraes in the metal weak tail of the thick disk. In the halo samples the distribution of V velocities is not gaussian, even when the metal weak thick disk stars are removed. Also, a plot of U and W velocities as a function of V velocity for the kinematically unbiased halo sample shows some curious structure. The cause of these kinematic anomalies is not clear. In addition, systematic changes to the distance scale within the range of currently accepted values of Mv(RR) are shown to significantly change the calculated halo kinematics. Fainter values of Mv(RR), such as those obtained by statistical parallax (~ 0.60 to 0.70 at [Fe/H]=-1.9), result in local halo kinematics similar to those reported in independent studies of halo kinematics, while brighter values of Mv(RR), such as those obtained through recent analysis of Hipparcos subdwarf parallaxes (~ 0.30 to 0.40 at [Fe/H]=-1.9), result in a halo with retrograde rotation and significantly enlarged velocity dispersions.

40 pages (including tables), 7 PostScript figures, accepted for publication in the Astronomical Journal

References in corpus (3)

• The Age Of Globular Clusters In Light Of Hipparcos: Resolving the Age Problem?
• Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
• Is There a Difference in Luminosity between Field and Cluster RR Lyrae Variables?

Cited by in corpus (35)

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• Kinematics of Metal-Poor Stars in the Galaxy. II. Proper Motions for a Large Non-Kinematically Selected Sample
• The Mass of the Milky Way: Limits from a Newly Assembled Set of Halo Objects
• Distance Scale Zero-Points from Galactic RR Lyrae Star Parallaxes
• A revision of the solar neighbourhood metallicity distribution
• Halo Star Streams in the Solar Neighborhood
• Metal Abundances and Kinematics of Bright Metal-Poor Giants Selected from the LSE Survey: Implications for the Metal-Weak Thick Disk
• Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-Metal" Stars - Confirmation of Metal-Poor Stars in the Thick Disk of the Galaxy
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• Spectroscopic Survey of the Galaxy with Gaia II. The expected science yield from the Radial Velocity Spectrometer
• A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations
• The Century Survey Galactic Halo Project III: A Complete 4300 deg^2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo
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• Astrometry with Hubble Space Telescope Fine Guidance Sensors - A Review
• Kinematic Structure in the Galactic Halo at the North Galactic Pole: RR Lyrae and BHB Stars show different kinematics
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• The Century Survey Galactic Halo Project II: Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars
• RR Lyrae stars: Kinematics, orbits and z-distribution
• Kinematics of Nearby Subdwarf Stars
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• The G-dwarf problem in the Galaxy
• Exploring the Galactic Anticenter substructure with LAMOST & Gaia DR2
• Abundances of metal-weak thick-disc candidates
• Two populations among the metal-poor field RR Lyrae stars
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