  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
combined 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 developed 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 lam5876, 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, which leads 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 disc. MWC 314 is a key system for
studying the evolutionary consequences of these effects.
