ИСТИНА

We consider the influence of the magnetic field of the O9.7 Iab supergiant component in the Cyg X-1 X-ray binary system on its atmosphere. In the frame of the simplest model (the unipolar cylindrically symmetric circum-polar magnetic spot model in static approximation, neglecting the Lorentz force component related to the force line curvature), the magnetic pressure is found to be comparable to model-atmosphere gas and radiative pressure, exceeding them in the area around the magnetic poles. As a result, bright spots are formed on the star surface. The dipolar or quadrupolar magnetic field can create large-size bright spots which can be studied by ground-based optical photometry. In the case of magnetic field inclined to the stellar rotation axis, resulting variability may be of the order of 1%. The field of higher multipolar configuration (produced by dynamo) can form smaller spots and may be detected only by space telescopes. Besides, the spots may be revealed from spectral-line profile variability. Multicolor or spectral observations of linear polarization also may be used for diagnostics of the optical component magnetic field. Observations of spots can be used as an instrument of magnetic field analysis.