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 effect, with Maximum I being 0.034 mag(V) and 0.030 mag(B) brighter than Maximum IS, 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 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 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.