AAS 205th Meeting, 9-13 January 2005
Session 142 Galactic Structure, Halo and High Velocity
Poster, Thursday, January 13, 2005, 9:20am-4:00pm, Exhibit Hall

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[142.10] Stellar Kinematics and Chemical Abundances at the Thick-Disk/Halo Interface

C. M. Rockosi (UCO/Lick Observatory), T. C. Beers (Michigan State), C. Allende-Prieto (UT), R. Wilhelm (Texas Tech), J. A. Munn (USNO)

The old stellar populations of the Milky Way carry the signature of their formation environment and dynamical history in their kinematics and chemical abundances. In particular, the dynamically hot thick disk and halo contain the oldest stars in the Galaxy, and are remnants of its more chaotic past. We present a study of the high-latitude thick disk and halo based on a uniformly-selected sample of over 3000 stars with available medium-resolution (2.3 Å) stellar spectra and ugriz photometry from the Sloan Digital Sky Survey. The stars occupy the main-sequence turnoff region of old populations and are selected without any kinematic or metallicity criteria, hence they provide an unbiased sample of the underlying stellar populations. This is the first one-third of a sample that will soon include on the order of 10,000 such stars.

We use radial velocities, proper motions, and estimates of [Fe/H], Teff, and log g to examine the rotation velocity, chemical abundance patterns, and velocity dispersions as a function of distance and position in the Galaxy. Based on these data, we examine the properties of the thick disk as a function of height above the Galactic plane and obtain a new estimate of the relative normalization of the thick disk and halo populations in the Galaxy.

This work received partial funding support from grant NASA grant HST-HF-01143.01-A and PHY 02-16783, Physics Frontier Centers/JINA: Joint Institute for Nuclear Astrophysics, awarded by the US National Science Foundation.

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