Anchoring the Population II Distance Scale: Accurate Ages for Globular Clusters and Field Halo Stars

Details Anchoring the Population II Distance Scale: Accurate Ages for Globular Clusters and Field Halo Stars Anchoring the Population II Distance Scale: Accurate Ages for Globular Clusters and Field Halo Stars

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...198.6309d&link_type=abstract

American Astronomical Society, 198th AAS Meeting, #63.09; Bulletin of the American Astronomical Society, Vol. 33, p.881

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As the oldest objects whose ages can be accurately determined, Galactic globular clusters can be used to establish the minimum age of the universe (and hence, to constrain cosmological models) and to study the early formation history of the Milky Way. The largest uncertainty in the determination of globular cluster ages is the distance scale. SIM will be able to determine distances to globular clusters and other stars in the halo with unprecedented accuracy, thereby significantly reducing the uncertainty in the derived ages of metal-poor stars. Our SIM key project will determine the distance scale to globulars and the ages of globular clusters and field halo stars with unprecedented accuracy. To establish the Population II distance scale and the ages of the metal-poor stars in our galaxy, three different observing strategies will be utilized: (1) direct parallax distances to 21 nearby globular clusters; (2) calibration of the luminosity of RR Lyrae stars in the field and in globular clusters; and (3) parallax distances to a sample of Population II main sequence turn-off and subgiant branch stars. The parallax observations of field turn-off and subgiant stars will lead to an accurate determination of the ages of these stars. The direct parallax distances to the nearest globular cluster will be the cornerstone of the observing strategy allowing us to set a firm lower limit to the age of the universe accurate to +/- 5% and to investigate the early formation history of the Milky Way. The calibration of the Population II distance scale will allow accurate distances to be obtained to a number of distant globular clusters and nearby galaxies and will help calibrate the zero point of the extragalactic distance scale.

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