EDP Sciences
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Volume 429, Number 2, January II 2005
Page(s) 645 - 655
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20041867

A&A 429, 645-655 (2005)
DOI: 10.1051/0004-6361:20041867

Eclipsing binaries as standard candles

HD 23642 and the distance to the Pleiades
J. Southworth, P. F. L. Maxted and B. Smalley

Department of Physics and Chemistry, Keele University, Staffordshire, ST5 5BG, UK
    e-mail: [jkt;pflm;bs]@astro.keele.ac.uk

(Received 20 August 2004 / Accepted 6 September 2004)

We present a reanalysis of the light curves of HD 23642, a detached eclipsing binary star in the Pleiades open cluster, with emphasis on a detailed error analysis. We compare the masses and radii of the two stars to predictions of stellar evolutionary models and find that the metal and helium abundances of the Pleiades are approximately solar. We present a new method for finding distances to eclipsing binaries, of spectral types A to M, using the empirical calibrations of effective temperature versus surface brightness given by Kervella et al. (2004, A&A, 426, 297). We use the calibration for K-filter surface brightness to determine a distance of  139.1  $\pm$ 3.5 pc to HD 23642 and the Pleiades. This distance is in excellent agreement with distances found from the use of theoretical and empirical bolometric corrections. We show that the determination of distance, both from the use of surface brightness relations and from the use of bolometric corrections, is more accurate and precise at infrared wavelengths than at optical wavelengths. The distance to HD 23642 is consistent with that derived from photometric methods and Hubble Space Telescope parallaxes, but is inconsistent with the distance measured using Hipparcos parallaxes of HD 23642 and of other Pleiades stars.

Key words: stars: distances -- stars: fundamental parameters -- stars: binaries: eclipsing -- stars: chemically peculiar -- Galaxy: open clusters and associations: general -- stars: binaries: spectroscopic

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