SDSS spectroscopic survey of stars

In addition to optical photometry of unprecedented quality, the Sloan Digital Sky Survey (SDSS) is also producing a massive spectroscopic database. We discuss determination of stellar parameters, such as effective temperature, gravity and metallicity from SDSS spectra, describe correlations between kinematics and metallicity, and study their variation as a function of the position in the Galaxy. We show that stellar parameter estimates by Beers et al. show a good correlation with the position of a star in the g-r vs. u-g color-color diagram, thereby demonstrating their robustness as well as a potential for photometric parameter estimation methods. Using Beers et al. parameters, we find that the metallicity distribution of the Milky Way stars at a few kpc from the galactic plane is bimodal with a local minimum at [Z/Zo]~ -1.3. The median metallicity for the low-metallicity [Z/Zo]<-1.3 subsample is nearly independent of Galactic cylindrical coordinates R and z, while it decreases with z for the high-metallicity [Z/Zo]> -1.3 sample. We also find that the low-metallicity sample has ~2.5 times larger velocity dispersion and that it does not rotate (at the ~10 km/s level), while the rotational velocity of the high-metallicity sample decreases smoothly with the height above the galactic plane.