NOAO >   Observing Info >   Approved Programs >   2001B-0211

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Proposal Information for 2001B-0211


PI: Andrew Dolphin, NOAO, dolphin@noao.edu
Address: Box 26732, Tucson, AZ 85726, USA

CoI: Abi Saha, NOAO
CoI: Evan Skillman, University of Minnesota
CoI: Jay Gallagher, University of Wisconsin
CoI: John Hoessel, University of Wisconsin
CoI: Ed Olszewski, University of Arizona

Title: Comparing the Primary Standard Candles in a Metal-Rich Galaxy: M31

Abstract: Our understanding of the extragalactic distance scale is limited in large part by uncertainties in the absolute magnitudes of the primary standard candles -- Cepheids and RR Lyraes. As these calibrations are largely independent (Cepheid calibrations are tied to the moving cluster distance to the Pleiades or an assumed LMC distance; RR Lyrae calibrations are tied to statistical parallax distances to globular clusters), a comparison between these indicates the degree of accuracy to which they are known. One such intercomparison has recently been done by us in the metal-poor galaxy IC 1613. M31 provides an ideal complementary case, since it has a higher central metallicity comparable to that of the galaxies observed in distance scale projects. When the results for IC 1613 and M31 are combined, it will shed light on the metallicity dependencies of the standard candles. While M31's Cepheid P- L relation is well-established, there are large uncertainties regarding its RR Lyrae p! opulation (both in terms of mean magnitude and number of stars) that must be resolved before such a comparison can be made.


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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