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

A new method for the determination of the grav- ity 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 Fre- quency Domain. In the analysis, the exponents for both compo- nents 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 previ- ous 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.