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N. De Lee (Michigan State), T.C. Beers (Michigan State & JINA), H.A. Smith, B. Marsteller, J. Krugler (Michigan State), Y. Lee (Michigan State & JINA), R. Wilhelm (Texas Tech), D. Terndrup (Ohio State)
We report on UBVRI CCD photometry that has been obtained over the course of the past seven years for a sample of over 1600 metal-poor (MP), field horizontal-branch (FHB), and other A-type candidates selected from two large objective-prism surveys, the HK survey of Beers and collaborators and the Hamburg/ESO stellar survey of Christlieb and colleagues. These stars either have, or soon will have, medium-resolution (1-2 Å) spectroscopy obtained with various 2.5m - 4m class telescopes, including the SOAR 4.1m.
These observations are being employed for several purposes. In the case of the FHB/A stars, the UBV photometry is useful for separating out low-gravity stars from the high-gravity ones. The subsample of high-gravity A-type stars includes Blue Metal Poor stars, halo and thick-disk blue stragglers, main-sequence A-type dwarfs, and Am and Ap stars. These observations are also being used to derive photometric distance estimates that will aid studies of high-velocity hydrogen clouds in the Galaxy, as well as to refine Galactic mass measurements. The data for the low-metallicity objects will be used to obtain estimates of temperatures that are required for elemental abundance studies based on future high-resolution spectroscopic observations, as well as to estimate distances for use in kinematic studies.
T.C.B. and Y.L. acknowledge partial support from grant AST 04-06784, as well as from grant PHY 02-16783, Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.