2005ApJ...635..502M

We study the K-correction for the case of emission lines formed in the X-ray-illuminated atmosphere of a Roche lobe-filling star. We compute the K-correction as a function of the mass ratio q and the disk flaring angle α using a compact binary code in which the companion's Roche lobe is divided into 10⁵ resolution elements. We also study the effect of the inclination angle in the results. We apply our model to the case of the neutron star low-mass X-ray binary X1822-371 (V691 CrA), where a K-emission velocity K_em=300±8 km/s has been measured by Casares et al. Our numerical results, combined with a previous determination of system parameters, yields 1.61 M_☉≤M_NS≤2.32 M_☉and 0.44 M_☉≤M₂≤0.56 M_☉for the two binary components (i.e., 0.24≤q≤0.27), which provide compelling evidence for a massive neutron star in this system. We also discuss the implications of these masses into the evolutionary history of the binary.