Abstract

Modeling the Asymmetrical Wind of the Massive LBV Binary MWC 314

Alex Lobel (Royal Observatory of Belgium)

J.H. Groh (MPI, Bonn, Germany), K. Torres (Univ. Sao Joao Del-Rei, Brazil), N. Gorlova (KU Leuven, Belgium), and C. Martayan (ESO, Chile)

Spectroscopic monitoring with Mercator-HERMES over the past two years reveals that MWC 314 is a massive binary system composed of an early B-type primary LBV star and a less-luminous supergiant companion. We determine an orbital period Porb=60.9 d from S II and Ne I absorption lines observed in this single-lined spectroscopic binary. We find a large amplitude of the radial velocity curve of 86.9 km/s around the systemic velocity of 30.5 km/s. The ASAS V light curve during our spectroscopic monitoring reveals two brightness minima (Delta V~0.1 mag.) over Porb that we attribute to partial eclipses at an orbital inclination angle of ~70 deg. The eclipsing massive binary model is supported by visual brightness maxima that coincide with the phases of largest and smallest radial velocity. We find a clear correlation between the orbital phases and the detailed shapes of optical and near-IR P Cygni-type line profiles of He I , Si II, and the double- or triple-peaked stationary cores of prominent emission lines of Fe II, etc. A preliminary 3-D radiative transfer model computed with Wind3D shows that the periodic P Cyg line profile variability results from an asymmetric common-envelope wind with enhanced density (or line opacity) in the vicinity of the LBV. The variable orientation of the inner LBV wind region due to the orbital motion produces P Cyg line profiles (with outflow velocities to ~200 km/s) between orbital phases phi=0.65 to 0.85, while weak inverse P Cyg profiles are observed Porb/2 later around phi~0.3. We do not observe optical or near-IR He II, C III, and Si III lines, signaling that the LBV's spectral type is later than B0. Detailed modeling of the asymmetrical wind properties of massive binary MWC 314 will provide important new physical information about the most luminous hot (binary) stars such as Eta Car.