Properties of galactic B[e] supergiants - III. MWC 300

We present the results of optical and near-IR spectroscopic and mid-IR imaging observations of the emission-line star MWC 300. Its properties and evolutionary state are still under debate (a B[e] supergiant or a Herbig Be star). For the first time we detected radial velocity variations of the photospheric lines and found a correlation between them and those of the He I lambda5876 Angstrom line. Most of the pure emission lines had stable positions for nearly 20 years. New estimates of the object's luminosity (log L/L. = 5.1 +/- 0.1), distance (D = 1.8 +/- 0.2 kpc), and systemic velocity (+26 +/- 2 km s(-1)) were derived. We found that both the circumstellar extinction in the disk-like dusty envelope and the interstellar extinction play a significant role in the attenuation of the stellar brightness. Our 2D modeling of the observed spectral energy distribution in the wavelength range from 0.3 mum to 1.3 mm suggests that the star is viewed through a gaseous-and-dusty flared disk with an opening angle of 30degrees, an inclination angle of 10degrees, an equatorial optical depth tau(V) = 3.0, and a total mass of 0.08 M.. We argue that MWC 300 is most likely a binary system, because of the similarities of its observed parameters with those of recognized B[e] binaries.