NOAO >   Observing Info >   Approved Programs >   2003B-0067

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Proposal Information for 2003B-0067


PI: Ignasi Ribas, Villanova University, iribas@ast.villanova.edu
Address: Astronomy Department, 800 Lancaster Ave., Villanova, PA 19085, USA

CoI: Edward F. Guinan, Villanova University
CoI: Ron Hilditch, University of St. Andrews
CoI: Carme Jordi, Universitat de Barcelona
CoI: Francesc Vilardell, Universitat de Barcelona

Title: The Cosmic Distance Scale: An Accurate Distance to M31 from Eclipsing Binaries

Abstract: M31 is potentially a crucial calibrator for the Cosmic Distance Scale, yet currently its distance is known to no better than ~15%. We have demonstrated in our work on the LMC and SMC distances that double-lined eclipsing binaries can serve as excellent ``standard candles''. Distances derived from eclipsing binaries are geometric and free from many assumptions that plague other less direct methods. Here we propose to extend our program to determine an accurate distance to M31. We have successfully obtained accurate light curves of suitable binaries and UV/optical spectrophotometry is planned for HST Cycle 12. The only missing ingredient to complete the analysis is medium- resolution spectroscopy to derive accurate radial velocities. In this pilot program we request Gemini-N GMOS multi-object spectroscopy of selected eclipsing binaries. The analysis of the radial velocity curves, when combined with the light curves and spectrophotometry, will yield accurate stellar masses, radii, luminosities, and distances. Based on our previous experience, we expect to reduce the uncertainty of the M31 distance to better than 5%, thereby firmly calibrating the Cosmic Distance Scale.


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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