Population III by Popular Demand - Progress and Previews

I discuss the ongoing search for stars of the Milky Way which have been referred to as members of Population III. Following a discussion of possible definitions for these stars, I consider the reasons why astronomers have undertaken this search, and list some of the numerous astrophysical uses of the extremely metal-poor stars found along the way. I then review survey techniques which have been used in the past, and provide an update on plans for future investigations. Finally, the question of when one might consider the search for Population III Finished is addressed.Comment: 12 pages, 0 figures, to appear in proceedings of THE FIRST STARS meeting, held in Garching, Germany, August 199

The Chemo-Dynamical History of the Milky Way as Revealed by SDSS/SEGUE

Although originally conceived as primarily an extragalactic survey, the Sloan Digital Sky Survey (SDSS-I), and its extensions SDSS-II and SDSS-III, continue to have a major impact on our understanding of the formation and evolution of our host galaxy, the Milky Way. The sub-survey SEGUE: Sloan Extension for Galactic Exploration and Understanding, executed as part of SDSS-II, obtained some 3500 square degrees of additional ugriz imaging, mostly at lower Galactic latitudes, in order to better sample the disk systems of the Galaxy. Most importantly, it obtained over 240,000 medium-resolution spectra for stars selected to sample Galactocentric distances from 0.5 to 100 kpc. In combination with stellar targets from SDSS-I, and the recently completed SEGUE-2 program, executed as part of SDSS-III, the total sample of SDSS spectroscopy for Galactic stars comprises some 500,000 objects. The development of the SEGUE Stellar Parameter Pipeline has enabled the determination of accurate atmospheric parameter estimates for a large fraction of these stars. Many of the stars in this data set within 5 kpc of the Sun have sufficiently well-measured proper motions to determine their full space motions, permitting examination of the nature of much more distant populations represented by members that are presently passing through the solar neighborhood. Ongoing analyses of these data are being used to draw a much clearer picture of the nature of our galaxy, and to supply targets for detailed high-resolution spectroscopic follow-up with the world's largest telescopes. Here we discuss a few highlights of recently completed and ongoing investigations with these data.Comment: 8 pages, 5 figures, to appear in IAU Symp. 26

Searches for the Most Metal-Poor Candidates from SDSS and SEGUE

We report on efforts to identify large samples of very and extremely metal-poor stars based on medium-resolution spectroscopy and ugriz photometry obtained during the course of the Sloan Digital Sky Survey (SDSS), and its extension, SDSS-II, which includes the program SEGUE: Sloan Extension for Galactic Understanding and Exploration. To date, over 8000 stars with [Fe/H] <= -2.0 and effective temperatures in the range 4500K < T_eff < 7000K have been found, with the expected numbers in this temperature range to be well over 10,000 once SEGUE is completed. The numbers roughly double when one includes warmer blue stragglers and Blue Horizontal-Branch (BHB) stars in these counts. We show the observed low-metallicity tails of the Metallicity Distribution Functions for the cooler SDSS/SEGUE stars obtained thus far. We also comment on the confirmation of an inner/outer halo dichotomy in the Milky Way, and on how this realization may be used to direct searches for even more metal-poor stars in the near future.Comment: 5 pages, 4 figures, from the conference "First Stars III", held in July 200

The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 square degrees of the southern high Galactic latitude sky. The candidate sample consists of 20,271 stars in the magnitude range 10 < B < 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known.Comment: 11 pages, 10 figures, accepted for publication in A&