AAS 203rd Meeting, January 2004
Session 112 The Milky Way and Its Environs
Poster, Thursday, January 8, 2004, 9:20am-4:00pm, Grand Hall

## [112.10] A Large, Fair", Sample of Halo and Thick Disk Stars from the SDSS

C. M. Rockosi (University of Washington), T. C. Beers (Michigan State University), C. Allende Prieto (University of Texas), R. Wilhelm (Texas Tech.), Sloan Digital Sky Survey Collaboration

The structure and evolution of the Milky Way is imprinted on the kinematics, chemical abundances, and spatial distribution of its constituent stars. In the past, samples of stars in the halo and thick disk have primarily been selected either on the basis of their kinematics (e.g., proper-motion selection), their distinct abundances (e.g., objective-prism selection of metal-poor stars), or their unusual colors (e.g., via \delta (U-B)). As a result, it has been difficult to confidently infer a unbiased picture of the underlying chemo-dynamical properties of the of these populations.

We present an analysis of the kinematics of the thick disk and the halo based on a sample of 1200 stars from two high-latitude fields for which we have measured radial velocities, proper motions, chemical abundances, and derived estimates of Teff and log(g), based on flux-calibrated medium-resolution spectroscopy and five-band ugriz photometry obtained from the Sloan Digital Sky Survey (SDSS). The stars are randomly chosen in the range g-r < 0.8, r < 19.15, and lie near the main-sequence turnoff of ancient stellar populations at distances between 1 and 10 kpc from the sun. They are selected without regard to their kinematics or chemical composition, and so represent a fair sample of the stellar populations from which they are drawn. We use this nearly ideal dataset to examine the correlation between kinematics, chemical abundance, and position in the Galaxy along these lines of sight. We compare the velocity and chemical abundance information with the global properties of the thick disk and halo as traced by the main-sequence turnoff color in the SDSS photometry, and with models for the thick disk and halo fit to SDSS color magnitude diagrams.

These data represent the first 10% of a much larger sample we are in the process of assembling. Future surveys of Galactic stars, such as might be obtained by the proposed SEGUE extension to SDSS, will enable unprecedented knowledge of the nature of the thick-disk, and the inner and outer halo populations of the Milky Way.

This work has received partial support from NSF grants AST 00-98508 and AST 00-98549 and NASA grant HST-HF-01143.01-A.

Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.