Spectral Classification and Estimation of Distances to the Be/X-Ray Binaries 1H1936+541 and 1H2202+501

Abstract

The results of the spectral and photometric studies of two Be/X-ray binaries, 1H1936+541 and 1H2202+501, are presented. The spectral class of the optical component of the 1H1936+541 system was determined for the first time, and the spectral class of the optical component of the 1H2202+501 system was refined. According to the results, the optical components of the systems 1H1936+541 and 1H2202+501 are Be stars of the spectral types B1Ve and B3Ve, respectively. These findings, as well as the well-known spectral type distribution of Be stars, can testify to the fact that the object 1H1936+541 belongs to X-ray binary systems. At the same time, taking into account the fact that a very small number of Be/X-ray binaries of the spectral type B3 is known so far, the object 1H2202+501 cannot unambiguously be classified as a Be/X-ray binary. The rotational speeds of the main components of these systems are 246 ± 11 km/s for 1H1936+541 and 111 ± 8 km/s for1H2202+501; the range of the tilt angles of their rotation axes is within 49°–82° and 21°–28°, respectively. Additionally, using the B and V band photometric observations and spectral classes obtained, the interstellar extinction values E(В – V), as well as the distances to the objects, were estimated. In particular, for 1H2202+501, the value of E(В – V) is 0.36 ± 0.03^m, and the distance r ranges from 0.8 to 1.6 kpc. For the 1H1936+541 system, the following values were obtained: E(В – V) = 0.23 ± 0.03^m and r = 2.1–3.6 kpc. The comparison of the distances to the objects with the data from the GAIA DR2 catalog (http://gea.esac.esa.int/archive/) revealed the coincidence of the corresponding values within the limits of errors.