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Astron. Astrophys. 344, 494-498 (1999)

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The kinematics of RR Lyrae stars observed by Hipparcos *

B. Chen

Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal 647, E-08028 Barcelona, Spain

Received 3 July 1998 / Accepted 9 December 1998

Abstract

We discuss the distributions of velocities and metallicities for 144 RR Lyrae stars observed by the Hipparcos astrometry satellite. The new absolute magnitude calibration of RR Lyrae stars and an all-sky reddening map have been used to derive individual distances accurately.

Three statistical analysis techniques based on pattern recognition theory are used to seek for significant signatures of stellar population characteristics in the sample. It is found that the intrinsic stellar distributions show a significant departure from a continuous trend, giving evidence for a discrete Galactic thick disk. Our results suggest that the disk and halo are separate kinematic structure without a smooth transition from one to the other.

Key words: methods: data analysis – stars: kinematics – stars: variables: RR Lyr – Galaxy: kinematics and dynamics – Galaxy: stellar content

* Based in part on observations made with ESA Hipparcos astrometry satellite

Send offprint requests to: bchen@mizar.am.ub.es

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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