NOAO >   Observing Info >   Approved Programs >   2002A-0232

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Proposal Information for 2002A-0232


PI: Bruce W. Carney, Univ. of North Carolina, bruce@physics.unc.edu
Address: CB\#3255, Chapel Hill, NC 27599-3255, USA

CoI: Andy McWilliam, Carnegie Observatories
CoI: David W. Latham, Center for Astrophysics
CoI: Brian Chaboyer, Dartmouth College

Title: Precise Ages of Halo Field Stars via Parallaxes & Chemistry

Abstract: The ages of subgiants in the field (and in clusters) may be estimated to high precision from high-quality parallax measures and chemical abundances, but with little sensitivity to the still uncertain helium abundances. We are part of a team that will undertake a key project with the Space Interferometer Mission to measure distances for about 80 metal-poor field subgiants (as well as about 60 field RR Lyrae variables and 21 globular clusters). Aside from accurate distances, the most critical variable in deriving absolute ages is the precision of the absolute and relative abundances. We propose to begin a long-term effort, but not with official long-term status, to improve the precision of the abundance determinations for our SIM targets. This proposal requests 4m/echelle observing time to study metal-poor field subgiants. The FAME and SIM missions will provide the required distance measurements. With abundance determinations determined to better than +/- 0.1 dex, \em obtained from a uniform body of spectra and atomic line data, we should be able to determine relative \em and absolute ages for individual field subgiant stars to a precision of about 5%.


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