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Proposal Information for 2003B-0081


PI: Bruce W. Carney, University of North Carolina, bruce@physics.unc.edu
Address: Dept. of Physics and Astronomy, Chapel Hill, NC 27599-3255, USA

CoI: Andy McWilliam, Carnegie Observatories
CoI: David W. Latham, Center for Astrophysics
CoI: Brian Chaboyer, Dartmouth College
CoI: John B. Laird, Bowling Green State University

Title: Halo Subgiants as Cosmological Probes

Abstract: Recent work on intergalactic deuterium abundances suggests that most of the Galactic halo star lithium abundances underestimate the Big Bang abundance of lithium. Halo \em subgiants may prove to be the best targets for the determination of the original lithium production during Big Bang nucleosynthesis (King et al. 1996) since they are cool yet have evolved from halo dwarfs with even shallower convection zones than stars still on the main sequence. Accurate abundances and distances may also be combined for subgiants to determine ages of individual stars, and this is independent of the still-uncertain helium abundance of the Galactic halo, unlike the case of main sequence turn-offs. We have completed three large surveys of almost 2000 field stars, from which we have identified 78 metal-poor field subgiants, and 43 primary targets for follow-up spectroscopy. The spectra, when added to a collection of similar observations of globular cluster red giants and horizontal branch stars, will enable us to put these field stars and cluster stars on a common abundance scale. Future high-precision distance determinations using NASA's Space Interferometer Mission will provide ages for these individual stars, if our abundances are of high precision. While SIM is six years from launch, we must \em complete the preliminary abundance work within the next two years to develop our final Key Project target list. This program has already begin at KPNO and will complement the same program for southern hemipshere stars now underway at Magellan.


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