Spectroscopic study of the optical counterpart to the Fast X-ray Transient IGR J17544-2619 based on observations at the 1.5-m RTT-150 telescope

TL;DR

This study uses spectroscopic observations to determine the orbital and physical parameters of the optical counterpart to the fast X-ray transient IGR J17544-2619, revealing the star is not a supergiant as previously believed.

Contribution

First spectroscopic determination of the binary system's parameters for IGR J17544-2619 using Doppler spectroscopy and non-LTE spectral modeling.

Findings

Optical star has $T_{eff}=33,000$ K, $ ext{log} ext{g}=3.85$, $R=9.5 R_{igodot}$, $M=23 M_{igodot}$.

Optical star is not a supergiant, contrary to previous assumptions.

Orbital and physical parameters of the binary system are now characterized.

Abstract

We present the results of our long-term photometric and spectroscopic observations at the Russian-Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy. We have computed theoretical spectra of the optical counterpart by applying non-LTE corrections for selected lines and obtained the parameters of the stellar atmosphere and the optical star ($T_{\rm eff}=33\,000$ K, $\log\,g=3.85$, $R=9.5\ R_{\odot},$ and $M=23\ M_{\odot}$). The latter suggest that the optical star is not a supergiant as has been thought previously.