Multicolor photoelectric WBVR observations of the close binary system HZ Her = Her X-1 in 1986-1988. Method and observations
We present results of four-color ( WBVR) photoelectric observations of the close binary HZ Her = Her X-1 in 1986-1988. As a rule, the duration of the observations exceeded two 35-day X-ray orbital periods in the 1986-1988 observing seasons. The accuracy and length of the photoelectric observations facilitated multi-faceted studies, which enabled us to define several fine photometric effects in the light curves of the binary more precisely and attempt to interpret them in a model for the matter flow from the optical component to the accretion disk around the neutron star. This model provides a satisfactory explanation for the inhomogeneity of the gas flow and "hot spot," as well as the existence of distinct "splashes" moving in their own Keplerian orbits around the outer parts of the Keplerian disk. We present series of light curves for all the observing seasons, as well as color-color diagrams that reflect the physics of various photometric effects. The transformation coefficients for each of the instrumental systems for the three observatories at which the observations were carried out are given. Atmospheric extinction was taken into account duringmulti-color observations of the object, with subsequent correction for atmospheric effects with accuracies ranging from 0.003 m to 0.005 m for air masses up to M( z) = 2.