High resolution optical spectroscopy of an LBV-candidate inside the CygOB2 association

Abstract

For the first time, we obtained the high-resolution (R=15000 and 60000) optical spectra for the extremely luminous star No.12, associated with the IR-source IRAS20308+4104, a member of the CygOB2 association. We have found about 200 spectral features in range 4552-7939AA, 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 spectral type is B5+/-0.5 Ia+. Our analysis of the Vr data shows the presence of a Vr gradient in the stellar atmosphere, caused by the infall of matter onto the star. The strong Halpha emission displays broad Thompson wings and time-variable core absorption, providing evidence that the stellar wind is inhomogeneous, and a slightly blue-shifted PCyg type absorption profile. We concluded that the wind is variable in time.