Masses of black holes in binary stellar systems

Mass determination methods and their results for ten black holes in X-ray binary systems are summarised. A unified interpretation of the radial velocity and optical light curves allows one to reliably justify the close binary system model and to prove the correctness of determination of the optical star mass function $f_{\mathrm v}(m)$.The orbit plane inclination $i$ can be estimated from an analysis of optical light curve of the system, which is due mainly to the ellipsoidal shape of the optical star (the so-called ellipticity effect). The component mass ratio $q=m_{\mathrm x}/m_{\mathrm v}$ is obtained from information about the distance to the binary system as well as from data about rotational broadening of absorption lines in the spectrum of the optical star. These data allow one to obtain from the value of $f_{\mathrm v}(m)$ a reliable value of the black hole mass $m_{\mathrm x}$ or its low limit, as well as the optical star mass $m_{\mathrm v}$. An independent estimate of the optical star mass $m_{\mathrm v}$ obtained from information about its spectral class and luminosity gives us test results. Additional test comes from information about the absence or presence of X-ray eclipses in the system. Effects of the non-zero dimension of the optical star, its pear-like shape, and X-ray heating on the absorption line profiles and the radial velocity curve are investigated. It is very significant that none of ten known massive ($m_{\mathrm x}>3M_{\odot}$) X-ray sources considered as black hole candidates is an X-ray pulsar or an X-ray burster of the first kind.