A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

Full space velocities are computed for a sample of 130 nearby RR Lyraevariables using both ground-based and Hipparcos proper motions. In many casesproper motions from multiple sources have been averaged to produce asignificant improvement in the transverse space velocity errors. In most cases,this exceeds the accuracy of Hipparcos proper motions alone. The velocityellipsoids computed for halo and thick disk samples are in agreement withprevious studies. No distinct sample of thin disk RR Lyraes has been isolatedbut there is kinematic evidence for some thin disk stars in our thick disksamples. A sample of 21 stars with [Fe/H] < -1.0 and disk-like kinematics havebeen isolated. It is concluded from their kinematics and spatial distributionthat these stars represent a sample of RR Lyraes in the metal weak tail of thethick disk. In the halo samples the distribution of V velocities is notgaussian, even when the metal weak thick disk stars are removed. Also, a plotof U and W velocities as a function of V velocity for the kinematicallyunbiased halo sample shows some curious structure. The cause of these kinematicanomalies is not clear. In addition, systematic changes to the distance scalewithin the range of currently accepted values of Mv(RR) are shown tosignificantly 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 independentstudies of halo kinematics, while brighter values of Mv(RR), such as thoseobtained through recent analysis of Hipparcos subdwarf parallaxes (~ 0.30 to0.40 at [Fe/H]=-1.9), result in a halo with retrograde rotation andsignificantly enlarged velocity dispersions.Comment: 40 pages (including tables), 7 PostScript figures, accepted for publication in the Astronomical Journa