Abstract. Complete light curves in B and V bands for YY Eridani are presented in this paper. The light curves appear to have a marked asymmetry with Max. I brighter than Max. II. Using the latest version of the WilsonDevinney light curve synthesis program, we have computed photometric solutions from the new light curves of YY Eri. The present solutions reveal that YY Eri is a W subtype contact binary. The asymmetries of the light curves are explained by the presence of dark spot on the primary or secondary component.

Abstract. Complete BV light curves of the W UMa type binary GZ And is presented in this paper. From the present times of minimum light and those collected from the references, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of GZ And continuously increased at a period change rate of dp p = 2.00 × 10 −10 . The observed orbital period increase of GZ And may be explained by a mass transfer rate from the smaller to the larger component of ∆m = 1.05 × 10 −7 M yr −1 . The present light curves are analyzed by means of the latest version of the Wilson-Devinney code. The results suggest that GZ And is a W-subtype W UMa contact binary with a mass ratio of 0.511. The present photometric mass ratio is in agreement with that obtained spectroscopically by Lu & Rucinski (1999). Combining the present photometric solution with the spectroscopic orbital elements by Lu & Rucinski (1999), we give absolute dimensions of GZ And. The determined masses and radii of the components show that GZ And is an unevolved main-sequence binary, but the luminosity of the primary is abnormally low for the same mass main-sequence star. The low luminosity of the primary may be explained by transformation between gravitational energy and thermal energy of the system.

Abstract. We present light curves and photometric solutions of the contact binary UY UMa in this paper. The light curves appear to exhibit a typical O'Connell effect, with Maximum I being 0.034 mag(V ) and 0.030 mag(B) brighter than Maximum II, respectively, and Maximum I shifting to phase 0.26. The light curves are analyzed by means of the latest version of the WD program. The results show that UY UMa is a W-subtype contact binary with a small mass ratio q = 0.134. The asymmetry of the light curves is explained by star spot models. From the collected data of 9 UMa contact systems with a smaller mass ratio than 0.20, the nature of the secondaries is analyzed. The results show that the luminosities and densities of the secondaries could be controlled by the primaries and that the smaller the mass ratio, the stronger the control.