ИСТИНА

We continue the study of photometric and spectral variability of Cyg X-1 based on the 40-year long series of multicolor photometric observations and the 12-year-long series of precise high-resolution spectral observations accumulated by us up to now. For the first time the optical component (O9.7Iab supergiant) temperature decrease and its size increase over 7 years (1997-2003) have been revealed in 2006. The photoelectric photometry performed at the SAI Crimean Station shows that the variability of the supergiant continues in the time scale of decades up to now. In average, the mean level of brightness decreases since 1999. The variations in time scale of a year superimpose on the light decay. There is a connection between X-ray and optical changes, which suggests that the overall drop is due to the temperature decrease of the supergiant, while its radius increases approaching a ctitical Roche lobe. This is a cause of unstable matherial flow and leads to frequent, non-irregular "hard" and "soft" X-ray changes. The variability of photospherical spectral line depths found in available high-resolution spectra is also in agreement with this idea. There are evidences of possible presence of a variable optical thin gas component. During an X-ray flare in 2009, we observed essential brightening in the U band, while it was absent in the B and V bands. This event may be result of appearance of a large amount of the hot optically thin gas component.