PHOTOMETRIC BEHAVIOR OF THE BINARY-SYSTEM CYG X-1 V1357 CYG DURING THE 1996 X-RAY OUTBURST

The results of photometric (UBV) and spectroscopic (H alpha) observati ons of the X-ray binary system Cyg X-1/V1357 Cyg performed during the 1996 X-ray outburst are presented. At the maximum of the outburst, the orbital light curve represented one wave over the period-there was no secondary minimum (inferior conjunction of the X-ray source). After t he completion of the outburst, the orbital light curve regained its no rmal shape that corresponded to the ellipticity effect. These changes were also accompanied by considerable changes in the profile and inten sity of the H alpha emission line: at the maximum of the outburst, the H alpha intensity was reduced. The yearly mean U, B, and V magnitudes of the object point to a secular increase in the luminosity of the su pergiant between 1971 and 1996 with a possible periodic component supe rimposed; its origin differs from that of the secular brightening. The anomalously high intensity of the 1996 X-ray outburst is attributable to an increase in the luminosity of the supergiant.