SIMBAD references

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.