Abstract
The Andromeda Galaxy (M31) is potentially a crucial calibrator for the cosmic distance scale and thus for determining the age and evolution of the Universe. Yet currently, the distance to M31 is known to no better than ∼ 15%. We have demonstrated in our work on the distance of the Large Magellanic Cloud that double-line eclipsing binaries can serve as excellent ``standard candles''. Distances derived from eclipsing binaries are basically geometric and essentially free from many assumptions and uncertainties that plague other less direct methods. We present the extension of our program of using eclipsing binaries as standard candles to determine an accurate distance to M31. The photometric observations that will provide the light-curves are under way with the Isaac Newton Telescope at the Roque de los Muchachos Observatory (La Palma). Spectrophotometric observations will be conducted with the Hubble Space Telescope, and large ground-based telescopes (for example, the GTC) will be necessary to acquire the spectra for the radial velocity curves because of the faintness of the target stars (V ∼ 19-20). Based on our previous experience, we expect to reduce the uncertainty of the distance of M31 to better than 5%, thereby firmly calibrating the cosmic distance scale.
