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 function of the mass ratio q and the disc flaring angle \alpha using a compact binary code where the companion ’ s Roche lobe is divided into 10 ^ { 5 } 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 \pm 8 km s ^ { -1 } has been measured by Casares et al .
( 2003 ) .
Our numerical results , combined with previous determination of system parameters , yields 1.61 M _ { \odot } \leq M _ { NS } \leq 2.32 M _ { \odot } and 0.44 M _ { \odot } \leq M _ { 2 } \leq 0.56 M _ { \odot } for the two binary components ( i. e . 0.24 \leq q \leq 0.27 ) , which provide a 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 .