The optical spectrum of an LBV candidate in the Cyg OB2 association

We have obtained the first high-spectral-resolution (R = 15 000 and 60 000) optical spectra for the extremely luminous star No. 12, identified with the IR source IRAS 20308+4104 in the Cyg OB2 association. We have identified about 200 spectral features at 4552-7939 Angstrom, including the interstellar NaI, KI lines and numerous DIBs, which are the strongest absorption lines in the spectrum, along with the HeI, CII, and SiII lines. A two-dimensional spectral classification indicates that the star's spectral type is B5+/-0.5 Ia(+). Our analysis of the radial-velocity pattern shows the presence of a radial-velocity gradient in the stellar atmosphere, due to the infall of matter onto the star. The strong Ha emission line displays broad Thompson wings and time-variable core absorption, providing evidence that the stellar wind is inhomogeneous, and a slightly blue-shifted P Cygni absorption profile. We Conclude that the wind is time-variable. (C) 2004 MAIK "Nauka/Interperiodica".