Photoelectric light curves of V566 Ophiuchi.

V 566 Oph is a W Ursac Majoris-type eclipsing binary system which undergoes complete eclipses; secondary eclipse is total. Approximately 2000 photoelectric observations of this system were obtained with B and V filters within a three-week interval in 1973. Observations covering the eclipse portions of the curves yielded eight epochs of minimum light. A study of all the available times of minimum light indicates that the period of the system, which had remained constant for at least 14 years, has increased. Single, well-defined curves were formed from the observations at each effective wavelength. The V curve is in agreement with the curve observed in 1966 by Bookmyer, but there is now a slight asymmetry in the secondary eclipse curve defined by the B observations that is not apparent in the 1966 curve. Solutions of the system based on the Russell model and on the centrally condensed Roche model are compared and discussed. Key words: photometry - W UMa systems - contact binaries - light-curve synthesis