WBVR observations of the X-ray star V1341 Cyg = Cyg X-2 in 1986-1992

We present the results of WBVR observations of the low-mass X-ray binary V1341 Cyg = Cyg X-2. Our observations include a total of 2375 individual measurements in four bands on 478 nights in 1986-1992. We tied the comparison and check stars used for the binary to the WBVR catalog using their JHK magnitudes. The uncertainty of this procedure was 3% in the B and V bands and 8%-10% for the W and R bands. In quiescence, the amplitude of the periodic component in the binary’s B brightness variations is within 0.265 ^m -0.278 ^m (0.290 ^m -0.320 ^m in W); this is due to the ellipsoidal shape of the optical component, which is distorted with gravitational forces from the X-ray component. Some of the system’s active states (long flares) may be due to instabilities in the accretion disk, and possibly to instabilities of gas flows and other accretion structures. The binary possesses a low-luminosity accretion disk. The light curves reveal no indications of an eclipse near the phases of the upper and lower conjunctions in quiescence or in active states during the observed intervals. We conclude that the optical star in the close binary V1341 Cyg = Cyg X-2 is a red giant rather than a blue straggler. We studied the longterm variability of the binary during the seven years covered by our observations. The optical observations presented in this study are compared to X-ray data from the Ginga observatory for the same time intervals.