UBVRI Photometric Study of the Totally Eclipsing Very Short Period W Ursae Majoris Binary GSC 2765-0348

ABSTRACT GSC 2765-0348 is a very short period ( P = 0.2835 d), solar type, G4V contact binary. Complete BVRI and partial U light curves covering the secondary eclipse are presented, along with a period study, surface temperature determination, and a simultaneous UBVRI light-curve solution. Our light curves show low-level ripples, surface activity, and asymmetries due to magnetic activity. Light curve amplitudes vary from 0.4-0.6 mag ( V) in the primary and secondary eclipses. The difference in adjacent maxima varies from ∼3-5%. Modeled results include two spot regions, one hot and one cool, both at equatorial positions of the primary, more massive component. A firm 34% fill-out and a small mass ratio of 0.31 is also determined. A total eclipse of 33 minutes is found to occur in the secondary eclipse, making GSC 2765-0348 a W-type (less massive star is hotter), W UMa variable.