PI: Bruce W. Carney, University of North Carolina, email@example.com
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
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 89 metal-poor field subgiants, and 58 primary targets for follow-up spectroscopy and, at a later date, high-precision distance determinations using NASA's Space Interferometer Mission. The work proposed here is fundamental to the final selection of targets for our SIM Key Project, and that work must be completed in advance of the General Observer proposal AO in 2005. We request observing time to continue a program begun already at KPNO, and which will complement the same program for southern hemipshere stars now underway at Magellan.
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