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 R _ { \sun } , an effective temperature of 18,100 K and a luminosity of 5 \times 10 ^ { 5 } L _ { \sun } .
These values are somewhat reduced compared to the stellar parameters of Wray~977 measured previously .
The deduced mass-loss rate and terminal velocity of the stellar wind are 10 ^ { -5 } M _ { \sun } yr ^ { -1 } and 305 km s ^ { -1 } , respectively .
The interstellar { Na \textsc { 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 luminosity derived from the model atmosphere is consistent with this distance ( 3 kpc ) .
The luminosity of the wind-fed X-ray pulsar ( L _ { X } \sim 10 ^ { 37 } erg s ^ { -1 } ) is in good accordance with the Bondi-Hoyle mass accretion rate .
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 \pm 3 km s ^ { -1 } yielding a mass ratio q = M _ { X } / M _ { opt } = 0.046 \pm 0.014 .
The absence of an X-ray eclipse results in a lower limit to the mass of Wray~977 of 39 M _ { \sun } .
An upper limit of 68 or 53 M _ { \sun } is derived for the mass of Wray~977 adopting a maximum neutron star mass of 3.2 or 2.5 M _ { \sun } , respectively .
The corresponding lower limit to the system inclination is i > 44 ^ { \circ } , supporting the view that the dip in the X-ray lightcurve is due to absorption by the dense stellar wind of Wray~977 ( ) .
The “ spectroscopic ” mass of Wray~977 is 43 \pm 10 M _ { \sun } , consistent with the range in mass derived from the binarity constraints .
The mass of the neutron star is 1.85 \pm 0.6 M _ { \sun } .
Time series of spectral lines formed in the dense stellar wind ( e.g . { He \textsc { i } } 5876 Å and H \alpha ) 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 .