Eclipsing Binaries in the Local Group: Calibration of the Zero-point of the Cosmic Distance Scale and Fundamental Properties of Stars in M31

Details Eclipsing Binaries in the Local Group: Calibration of the Zero-point of the Cosmic Distance Scale and Fundamental Properties of Stars in M31 Eclipsing Binaries in the Local Group: Calibration of the Zero-point of the Cosmic Distance Scale and Fundamental Properties of Stars in M31

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hst..prop10578r&link_type=abstract

HST Proposal ID #10578

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Hst Proposal Id #10578 Hot Stars

Scientific paper

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 M31 distance modulus { 750 kpc} is is still uncertain to within 0.1-0.15 mag. We have demonstrated in our work on the LMC distance that double-lined 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, such as metallicity differences and calibration zeropoints. The absolute radii of the component stars of eclipsing binaries can be determined to better than a few percent from the time-tested analyses of their light and radial velocity curves. With accurate radii and temperatures, it is possible to determine reliable distances. We are extending our program of using eclipsing binaries as standard candles to determine an accurate distance to M31. As a first step, we are proposing to carry out HST spectroscopy of two carefully selected 19th mag early-B eclipsing binaries in M31. HST/ACS prism/grism low-resolution spectrophotometry {115-900 nm} is only missing key element of this program and is used to determine reliable values for T_eff, [Fe/H], and ISM extinction. These quantities, when combined with the results from our existing light and radial velocity curves for the two targets, will yield the stellar masses, radii, luminosities, and, importantly, the distances. The resulting fundamental stellar properties will be the first determined for stars in M31. Based on our previous experience, we expect to reduce the uncertainty of the M31 distance to better than 5%, thereby leading to a firmer calibration of the Cosmic Distance Scale and the zeropoint of H_0.

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