The “K‐Correction” for Irradiated Emission Lines in LMXBs: Evidence for a Massive Neutron Star in X1822−371 (V691 CrA)

We study the K-correction for the case of emission lines formed in the X-rayilluminated atmosphere of a Roche lobe filling star. We compute theK-correction as function of the mass ratio 'q' and the disc flaring angle'alpha' using a compact binary code where the companion's Roche lobe is dividedinto 10^5 resolution elements. We also study the effect of the inclinationangle in the results. We apply our model to the case of the neutron starlow-mass X-ray binary X1822-371 (V691 CrA), where a K-emission velocityK_em=300 +-8 km/s has been measured by Casares et al. (2003). Our numericalresults, combined with previous determination of system parameters, yields1.61Msun < M_NS < 2.32Msun and 0.44Msun < M_2 < 0.56Msun for the two binarycomponents(i. e. 0.24 < q < 0.27), which provide a compelling evidence for amassive neutron star in this system. We also discuss the implications of thesemasses into the evolutionary history of the binary.Comment: 6 pages, 5 figures. Accepted for publication in Ap