Masses of optical components and black holes in x-ray novae: the effects of components proximity
Abstract
An exact calculation of CaI λ 6439.075A absorption profiles in the spectra of optical stars in low-mass X-ray binary systems with black holes (BH LMXBs) is carried out. We show that the approximation of a real Roche lobe filling star as disk with uniform local line profile and linear limb darkening law leads to overestimation of projected equatorial rotational velocity Vrot i and accordingly, underestimation of mass ratio q=Mx/Mv. Refined value of q does not affect the mass of a black hole, but the mass of an optical star has shrunk 1.5 times. We present refined components masses in low-mass X-ray binaries with black holes. Companion masses in BH LMXBs are found in the mass range 0.1 - 1.6 M with the peak at Mv 0.35 M. This finding poses additional problem for the standard evolutionary scenarios of BH LMXBs formation with a common envelope phase (CE). We also discuss the implications of these masses into the evolutionary history of the binary.