Results of high-resolution optical spectroscopy investigation of Cyg X-1 = V1357 Cyg

Selected results of optical high-resolution spectral observations (in 1997 and 2002–2004) are briefly reviewed. A comparison with ASM/RXTE X-ray data is made. The photometric and spectral variations point to supergiant parameter changes on a timescale of tens of years. Line profile non-local thermodynamic equilibrium simulations lead to the conclusion that the star radius increased about 1–4% from 1997 to 2003–2004 and the temperature decreased by 1300–2400 K.