Thick disk kinematics from RAVE and the solar motion^⋆

¹ University College London, Department of Space & Climate Physics, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking Surrey RH5 6NT, UK
e-mail: sp2@mssl.ucl.ac.uk
² Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12−14, 69120 Heidelberg, Germany
³ University of Ljubljana, Faculty of Mathematics and Physics, 1000 Ljubljana, Slovenia
⁴ Center of Excellence SPACE-SI, Aškerčeva cesta 12, 1000 Ljubljana, Slovenia
⁵ Department of Physics and Astronomy “G. Galilei”, Padova University, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁶ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ Observatoire astronomique de Strasbourg 11 rue de l’Université, 67000 Strasbourg, France
⁸ Sydney Institute for Astronomy, University of Sydney, NSW 2006, Australia
⁹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK
¹⁰ Monash Centre for Astrophysics, Monash University, Clayton 3800 Australia
¹¹ Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK
¹² University of Victoria, Department of Physics and Astronomy, Victoria, BC Canada V8P 5C2
¹³ Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia
¹⁴ Macquarie research centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University NSW 2109, Australia
¹⁵ Australian Astronomical Observatory, PO Box 296, Epping, NSW 2121, Australia
¹⁶ Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 23 April 2012
Accepted: 24 August 2012

Abstract

Context. Radial velocity surveys such as the RAdial Velocity Experiment (RAVE) provide us with measurements of hundreds of thousands of nearby stars most of which belong to the Galactic thin, thick disk or halo. Ideally, to study the Galactic disks (both thin and thick) one should make use of the multi-dimensional phase-space and the whole pattern of chemical abundances of their stellar populations.

Aims. In this paper, with the aid of the RAVE survey, we study the thin and thick disks of the Milky Way, focusing on the latter. We present a technique to disentangle the stellar content of the two disks based on the kinematics and other stellar parameters such as the surface gravity of the stars. Using the Padova Galaxy model, we checked the ability of our method to correctly isolate the thick disk component from the Galaxy mixture of stellar populations.

Methods. We introduce selection criteria in order to clean the observed radial velocities from the Galactic differential rotation and to take into account the partial sky coverage of RAVE. We developed a numerical technique to statistically disentangle thin and thick disks from their mixture.

Results. We deduce the components of the solar motion relative to the local standard of rest (LSR) in the radial and vertical direction, the rotational lag of the thick disk component relative to the LSR, and the square root of the absolute value of the velocity dispersion tensor for the thick disk alone. The analysis of the thin disk is presented in another paper. We find good agreement with previous independent parameter determinations. In our analysis we used photometrically determined distances. In the Appendix we show that similar values can be found for the thick disk alone as derived in the main sections of our paper even without the knowledge of photometric distances.