. The black hole X-ray binary V404Cyg was studied during of the 2015 outburst. Optical photometry and spectroscopy were performed by using 1.5-meter Russian-Turkish telescope (RTT-150) facilities at the TUBITAK National Observatory (Antalya, Turkey). From June 22 to June 28, 2015, shell expansion velocity decreased from 650 to 400 km s–1 as measured by Hα and Hβ lines and from 450 to 330 km s–1 as measured by HeI and HeII lines. Thus, the shell expansion occurred with deceleration, where the hydrogen and helium line formation regions are at different radial distances from the center of the star. The correlation of flow variability in the optical and X-ray ranges is caused by fluctuations in the rate of accretion near a compact source where X-ray photons are generated.
