Orbital parameters of the high-mass X-ray binary 4U 2206+54

We present new radial velocities of the high-mass X-ray binary star 4U 2206+54 based on optical spectra obtained with the Coudé spectrograph at the 2 m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria in the period November 2011-July 2013. The radial velocity curve of the He I λ6678 Å line is modeled with an orbital period P_orb = 9.568 d and an eccentricity of e = 0.3. These new measurements of the radial velocity resolve the disagreements of the orbital period discussions.

Based on observations obtained with the 2 m RCC telescope at Rozhen NAO, Bulgaria.