Modeling of the optical spectra of the High-mass X-ray binaries IGR J17544-2619 and IGR J21343+4738

<p>We present the results of our long-term photometric and spectroscopic observations at the Russian&ndash;Turkish RTT-150 telescope for the optical counterparts of the High-mass X-ray binaries IGR J17544-2619 and IGR J21343+4738. Based on our optical data, we have determined for the first time the orbital and physical parameters of the IGR J17544-2619 by the methods of Doppler spectroscopy. We have calculated theoretical spectra for the optical counterpart by applying non-LTE corrections for selected lines and obtained the parameters of the stellar atmosphere (<em>T</em>_eff = 33 000 K, log <em>g</em> = 3.85, <em>R_V&nbsp;</em>= 9.5 R_sun, and <em>M_V</em> = 23M_sun). The variability of the H&alpha; line in the optical Be star spectra of the IGR J21343+4738 is studied. It reflects the dynamic evolution of the equatorial disk of the optical star. Decrease of the equivalent width of the central absorption of the H&alpha; line from 2006 to 2012 and from 2014 to 2019 is accompanied by a decrease in the photometric brightness of the system, which is explained by an increase in the radius of the equatorial disk of the Be star, which eclipses the star itself. In 2013, the disk size reached its maximum value and was destroyed. From 2014 to 2019 the process of accumulation of matter again began in the equatorial disk of the star, and it can be assumed that in the near future the source will again flare up in the X-ray range.</p>