Revised Parameter Estimates For The Most Metal-Poor Candidates In SDSS-I And SEGUE

There are several hundred thousand R = 2000 stellar spectra reported in the final public release of the Sloan Digital Sky Survey (SDSS-I) and the continuing project SEGUE (Sloan Extension for Galactic Exploration and Understanding), which has completed roughly half of its scheduled set of observations to date.The stars in this sample were targeted for a wide variety of reasons, and hence do not represent a sample from which an unbiased metallicity distribution function (MDF) of stars in the halo or thick-disk populations may be drawn. However, there exist over 6500 stars with estimated metallicities [Fe/H] < -2.0 and effective temperatures in the range 4500 K < Teff < 7000 K among this sample, based on application of the SDSS/SEGUE spectroscopic parameter analysis pipeline. We have continued to refine estimates of the stellar parameters for these stars, using an automated synthetic spectrum approach, autoMOOG. This technique produces estimates of [Fe/H] as well as [C/Fe] (or upper limits on these quantities) based on MOOG syntheses of the region of spectrum around the CaII K line and the CH G band, respectively.This sample represents, by a factor of more than three, the largest database of very metal-poor stars yet assembled. A least 1000 of these stars have g < 16.5, and hence are amenable to high-resolution spectroscopic studies with presently available large-aperture telescopes.