The Ages of Globular Clusters and the Population II Distance Scale

Details The Ages of Globular Clusters and the Population II Distance Scale The Ages of Globular Clusters and the Population II Distance Scale

Feb 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009noao.prop....9h&link_type=abstract

NOAO Proposal ID #2009A-0009

Astronomy and Astrophysics

Astronomy

Scientific paper

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.

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