UY Ursae Majoris: A W-subtype WUMa system with a small mass ratio

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 e ffect, with Maximum I being 0.034 mag(V) and 0.030 mag(B) brighter than Max imum IS, respectively, and Maximum I shifting to phase 0.26. The light curv es are analyzed by means of the latest version of the WD program. The resul ts show that UY Uh la 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 mod els. From the collected data of 9 UMa contact systems with a smaller mass r atio than 0.20. the nature of tile secondaries is analyzed. The results sho w that tile luminosities and densities of the secondaries could be controll ed by the primaries and that the smaller the mass ratio; the stronger the c ontrol.