  Model atmosphere fits to high-resolution optical spectra of Wray 977 confirm
the B hypergiant classification of the massive companion to the X-ray pulsar
GX301-2. The models give a radius of 62 Rsun, an effective temperature of
18,100 K and a luminosity of 5 x 10^^5 Lsun. The deduced mass-loss rate and
terminal velocity of the stellar wind are 10^^-5 Msun/yr and 305 km/s,
respectively. The interstellar Na I D absorption indicates that Wray 977 is
located behind the first intersection with the Sagittarius-Carina spiral arm
(1-2.5 kpc) and probably belongs to the stellar population of the Norma spiral
arm at a distance of 3-4 kpc. The spectra obtained with UVES on the Very Large
Telescope (VLT) cover a full orbit of the system, including periastron passage,
from which we derive the radial-velocity curve of the B hypergiant. The
measured radial-velocity amplitude is 10 +/-3 km/s yielding a mass ratio q =
0.046 +/- 0.014. The absence of an X-ray eclipse results in a lower limit to
the mass of Wray 977 of 39 Msun. An upper limit of 53 Msun is derived for the
mass of Wray 977 adopting a maximum neutron star mass of 2.5 Msun. The
``spectroscopic'' mass of Wray 977 is 43 +/- 10 Msun, consistent with the range
in mass derived from the binarity constraints. The mass of the neutron star is
1.85 +/- 0.6 Msun. Time series of spectral lines formed in the dense stellar
wind indicate the presence of a gas stream trailing the neutron star in its
orbit. The long-term behaviour of the H alpha equivalent width exhibits strong
variations in wind strength; the sampling of the data is insufficient to
conclude whether a relation exists between wind mass-loss rate and pulsar spin
period.
