NOAO >   Observing Info >   Approved Programs >   2009A-0009

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Proposal Information for 2009A-0009


PI: Thomas E Harrison, New Mexico State University, tharriso@nmsu.edu
Address: Astronomy Department, Box 30001/MSC4500, Las Cruces, NM 88003, USA

CoI: Brian Chaboyer, Dartmouth College
CoI: G. Fritz Benedict, University of Texas, Austin
CoI: Ata Sarajdini, University of Florida
CoI: Ryan Campbell, NOAO/CTIO

Title: The Ages of Globular Clusters and the Population II Distance Scale

Abstract: Globular clusters are the oldest objects in the universe whose age can be accurately determined. The dominant error in globular cluster age determinations is the uncertain Population II distance scale. We have an accepted HST Cycle 17 & 18 program (108 orbits) to obtain parallaxes with an accuracy of +/-0.2 milliarcsecond for nine main sequence stars with [Fe/H] < -1.5. This will determine the absolute magnitude of these stars with accuracies of 0.04 to 0.06 mag. These data will be used to determine the distance to 24 metal-poor globular clusters using main sequence fitting. These distances (with errors of +/-0.05 mag) will be used to determine the ages of globular clusters using the luminosity of the subgiant branch as an age indicator. As in previous HST FGS astrometry programs, we require optical spectra and photometry to properly classify the stars used in our reference frame. This proposal seeks time on both the KPNO and CTIO 4m to obtain spectra of the reference stars in the nine target fields for MK classification. We request service observing on the CTIO 0.9m for photometry of one field that is unreachable from New Mexico.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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