PHOTOMETRIC OBSERVATIONS OF HIGH MASS X-RAY BINARY HD 226868

Abstract

The results of photometric observations of the high mass X-ray binary HD 226868 = Cyg X-1 have been presented. The observations of this star were performed at 60-cm telescope of ShAO named after N.Tusi by using CCD photometer. This star is a binary system consisting of a black hole and a massive giant component star. Black hole and optical giant component
masses are M = 20 ± 5M_⊙ and M_opt = 40 ± 5M_⊙, respectively. The blue supergiant orbiting the black hole is HDE 226868 and its spectral type is O9.7 Iab. Our aim was investigating variability of this star in the V filter of the BVRI photometric system. Together with our photometric observations we used also AAVSO photometric database for the star HD 226868. Short-term and long-term photometric variability of this star has been revealed. The low luminosity state of star HD 226868 was discovered by analyzing the AAVSO photometric database, where V magnitude changes in the interval between ∼ 9^m.1 and 9^m.2. The lower luminosity state was observed on November 16, 2021, from 19^h 55^m 12^s to 20^h 11^m 02^s. This state may be related to the supergiant wind instability as well as changes in the supergiant’s mass transfer rate.