Medium resolution spectroscopy of the supergiant O3If* Cyg OB2 No7

We examine the feasibility of using medium resolution spectra for determining the parameters of atmospheres of hot stars by means of numerical simulations. We chose the star Cyg OB2 No7 as a test object and obtained its spectrum (\lambda/\Delta\lambda=2500) with Russian-Turkish RTT150 telescope. The CMFGEN code was used to construct a model of the atmosphere of Cyg OB2 No7. For the first time we have detected the NIV \lambda\lambda 7103.2-7129.2 lines in the spectrum of this star and used them to determine the physical parameters of the wind. The rate of mass loss measured using the H$\alpha$ line exceeds the loss rate measured using lines formed in the wind. This indicates that the wind is nonuniform, apparently due to rotation.