ИСТИНА

Preliminary results of broad-band photometric observations of low-mass X-ray binary Her X-1/HZ Her carried out during the summer 1999 when the system comes to an extended low state of activity are presented. UBV monitoring of Her X-1 was fulfilled as a part of an extensive observational program of optical study of unique astrophysical objects carrying out at Sternberg Astronomical Institute. The data presented in this paper were mostly obtained on the binary phases 0.93-1.07 (X-ray eclipse). The anomalous low-state of the X-ray flux from Her X-1 was also detected only in 1983 and 1993. Our new observations were analysed with the goal to find some evidence for pecularities in the optical behavior of Her X-1 during such states and variations in the accretion disc structure. The 1999 data clearly show that the brightness of the accretion disc in Her X-1 at the X-ray eclipse ingress/egress is significantly less than the average brightness of this system in the main on-state derived early by Voloshina and Lyuty (1989). The changes in conditions of the X-ray irradiation of the optical star in Her X-1 were also considered. The color index behavior on two-color diagram (U-B)-(B-V) is discussed. The results obtained can be explained by variations of the optical characteristics of the accretion disc radiation in Her X-1. These variations are possibly connected with a decrease of the accretion disc inclination with respect to the orbital plane in the frame of the model invoking a twisted tilted accretion disc around the central neutron star (Sheffer et al., 1988).