Modelling the asymmetric wind of the luminous blue variable binary MWC 314


A. Lobel (1), J. H. Groh (2), C. Martayan (3), Y. Fremat (1), K. Torres Dozinel (4), G. Raskin (5), H. Van Winckel (5), S. Prins (5), W. Pessemier (5), C. Waelkens (5), H. Hensberge (1), L. Dumortier (1), A. Jorissen (6), S. Van Eck (6), and H. Lehmann (7)

(1) Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium
(2) Geneva Observatory, Geneva University, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland
(3) European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
(4) University of Sao Joao Del Rei, CAP, 36420-000 Ouro Branco, MG, Brazil
(5) University of Leuven, Instituut voor Sterrenkunde, Celestijnenlaan 200 D, B-3001 Heverlee, Belgium
(6) Universite Libre de Bruxelles, Boulevard du Triomphe, B-1050, Brussels, Belgium
(7) Thuringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany

We present a spectroscopic analysis of MWC 314, a luminous blue variable (LBV) candidate with an extended bipolar nebula. The detailed spectroscopic variability is investigated to determine if MWC 314 is a massive binary system with a supersonically accelerating wind or a low-mass B[e] star. We compare the spectrum and spectral energy distribution to other LBVs (such as P Cyg) and find very similar physical wind properties, indicating strong kinship.
We combine long-term high-resolution optical spectroscopic monitoring and V-band photometric observations to determine the orbital elements and stellar parameters and to investigate the spectral variability with the orbital phases. We develop an advanced model of the large-scale wind-velocity and wind-density structure with 3-D radiative transfer calculations that fit the orbitally modulated P Cyg profile of He I lamb5876, showing outflow velocities above 1000 km/s.
We find that MWC 314 is a massive semi-detached binary system of ~1.22 AU, observed at an inclination angle of i=72.8 deg. with an orbital period of 60.8 d and e=0.23. The primary star is a low-vsini LBV candidate of m1=39.6 Msun and R1=86.8 Rsun. The detailed radiative transfer fits show that the geometry of wind density is asymmetric around the primary star with increased wind density by a factor of 3.3, leading the orbit of the primary. The variable orientation causes the orbital modulation that is observed in absorption portions of P Cyg wind lines. Wind accretion in the system produces a circumbinary disc.
MWC 314 is in a crucial evolutionary phase of close binary systems, when the massive primary star has its H envelope being stripped and is losing mass to a circumbinary disk. MWC 314 is a key system for studying the evolutionary consequences of these effects.

Reference: Astronomy and Astrophysics, Main Journal
Status: Manuscript has been accepted

Weblink: http://dx.doi.org/10.1051/0004-6361/201220421

Comments: http://arxiv.org/abs/1308.4638

Email: Alex.Lobel@oma.be