Properties of galactic B[e] supergiants - II. HDE 327083

The emission-line object HDE 327083 has long been considered to be one of the most luminous stars in the Milky Way. Nevertheless, no reliable physical parameters have been published for it. Our high-resolution optical spectroscopy revealed the presence of photospheric lines of a cool luminous companion. We detected significant antiphased radial velocity variations of the emission and absorption lines. The data obtained are still insufficient to derive a reliable orbital solution; however, the orbital period is most likely of the order of 6 months. We conclude that HDE 327083 is a binary system consisting of an early B-type primary and early F-type secondary, with luminosities log L/L-. = 5.0 +/- 0.4 and 4.2 +/- 0.4, respectively, and whose orbital plane is viewed nearly edge-on. We also obtained new multicolour optical and infrared photometry of HDE 327083. From both the photometric and spectroscopic data, we found that the system is located at a distance of 1.5 +/- 0.5 kpc. Most of the circumstellar gas seems to be orbiting the primary and is distributed in a mildly flattened envelope with a height scale and velocity decreasing outward from the star. We suggest that HDE 327083 represents an advanced evolutionary stage of a beta Lyrae type binary.