STScI Preprint #1316
We present a detailed description of the magnitude, color, kinematics and geometry of the stellar populations in the solar neighborhood, as derived from the blue half of the Hipparcos Catalogue (0<B-V<0.8). In our presentation, the HR diagram is divided into three main components: a narrow main sequence, a broader and brighter component representing stars just evolving from the main sequence, and the luminous stars, which represent a continuum from subgiants to supergiants. Velocity-wise, three separate components are also needed: a young population with very low velocity dispersion (r~20-25 km/s), an older disk population (r~30-50 km/s), and the very high velocity component, which includes the spheroid/halo population and possibly also the thick disk.
1)ESA/Space Telescope Science Institute, on assignment from the
Space Sciences Division of the European Space Agency
2)Carnegie Mellon University