The optical behavior of the Be star in the high-mass X-ray transient A0535+26/HDE245770 shows that at periastron the luminosity is typically enhanced by 0.02 to a few tenths mag, and the X-ray outburst occurs eight days after the periastron. We constructed a quantitative model for this event based on a nonstationary accretion disk behavior, connected with a high ellipticity of the orbital motion. We explain the observed time delay between the peaks of the optical and X-ray outbursts in this system by the time of radial motion of the matter in the accretion disk, after an increase of the mass flux in the vicinity of a periastral point in the binary. This time is determined by the turbulent viscosity with a parameter of α = 0.1−0.3. The increase of the mass flux is a sort of flush that reaches the external part of the accretion disk around the neutron star, which enhances the optical luminosity. The subsequent X-ray flare occurs when the matter reaches the hot central parts of the accretion disk and the neutron star's surface.

The problem of steady-state accretion to nonrotating black holes is examined. Advection is included and generalized formulas for the radiation pressure in both the optically thick and thin cases are used. Special attention is devoted to models with a high accretion rate. Global solutions for accretion disks are studied which describe a continuous transition between an optically thick outer region and an optically thin inner region. It is shown that there is a maximum disk temperature for the model with a viscosity parameter

The optical behaviour of the Be star in the high mass X-ray transient A0535+26/HDE245770 shows that at the periastron typically there is an enhancement in the luminosity of order 0.05 to few tenths mag, and the X-ray outburst happens about 8 days after the periastron. We construct a quantitative model of this event, basing on a nonstationary accretion disk behavior, connected with a high ellipticity of the orbital motion. We explain the observed time delay between the peaks of the optical and X-ray outbursts in this system by the time of radial motion of a matter in the accretion disk, after increase of the mass flux in the vicinity of a periastral point in the binary. This time is determined by the turbulent viscosity, with the parameter α = 0.1 − 0.3, estimated from the comparison of the model with observational data