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Absolute dimensions of detached eclipsing binaries – I. The metallic-lined system WW Aurigae


E-mail: (JS); (PFLM); (BS); (AC); (PBE)


WW Aurigae is a detached eclipsing binary composed of two metallic-lined A-type stars orbiting each other every 2.5 d. We have determined the masses and radii of both components to accuracies of 0.4 and 0.6 per cent, respectively. From a cross-correlation analysis of high-resolution spectra we find masses of 1.964 ± 0.007 M for the primary star and 1.814 ± 0.007 M for the secondary star. From an analysis of photoelectric uvby and UBV light curves we find the radii of the stars to be 1.927 ± 0.011 R and 1.841 ± 0.011 R, where the uncertainties have been calculated using a Monte Carlo algorithm. Fundamental effective temperatures of the two stars have been derived, using the Hipparcos parallax of WW Aur and published ultraviolet, optical and infrared fluxes; these are 7960 ± 420 and 7670 ± 410 K. The masses, radii and effective temperatures of WW Aur are only matched by theoretical evolutionary models for a fractional initial metal abundance, Z, of approximately 0.06 and an age of roughly 90 Myr. This seems to be the highest metal abundance inferred for a well-studied detached eclipsing binary, but we find no evidence that it is related to the metallic-lined nature of the stars. The circular orbit of WW Aur is in conflict with the circularization time-scales of both the Tassoul and the Zahn tidal theories and we suggest that this is due to pre-main-sequence evolution or the presence of a circular orbit when the stars were formed.