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Astron. Astrophys. 335, 199-206 (1998)

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An observational approach for the determination of gravity darkening in contact binaries of W UMa type

G. Pantazis and P.G. Niarchos

Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Athens, Panepistimiopolis, GR-15784 Zografos, Athens, Greece

Received 7 January 1998 / Accepted 20 March 1998


A new method for the determination of the gravity darkening exponents in close binaries of W UMa type is presented. The method is based on Kopal's method of Fourier analysis of the light changes of eclipsing variables in the Frequency Domain. In the analysis, the exponents for both components of a W UMa system are assumed to be the same. First, the method was successfully applied to two theoretical (test) light curves, belonging to two systems with radiative and convective envelopes, respectively. Then the method was applied to 36 W UMa systems for which geometric and photometric elements have been derived by the most powerful techniques. Systems showing large light curve anomalies were excluded from the analysis, since the effectiveness of the method depends strongly on the quality of the observations. Our results confirm the previous results with the assumed, same geometrical parameters.The derived values of the gravity darkening exponents are very close to the predicted ones by the existing theory of radiative transfer or convective equilibrium.

Key words: stars: atmospheres – stars: binaries: eclipsing – stars: fundamental parameters

Send offprint requests to: P.G. Niarchos

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© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998