We present new results from a study of high quality , red spectra of the massive binary star system HD 1383 ( B0.5 Ib + B0.5 Ib ) .
We determined radial velocities and revised orbital elements ( P = 20.28184 \pm 0.0002 d ) and made Doppler tomographic reconstructions of the component spectra .
A comparison of these with model spectra from non-LTE , line blanketed atmospheres indicates that both stars have almost identical masses ( M _ { 2 } / M _ { 1 } = 1.020 \pm 0.014 ) , temperatures ( T _ { eff } = 28000 \pm 1000 K ) , gravities ( \log g = 3.25 \pm 0.25 ) , and projected rotational velocities ( V \sin i \lesssim 30 km s ^ { -1 } ) .
We investigate a number of constraints on the radii and masses of the stars based upon the absence of eclipses , surface gravity , stellar wind terminal velocity , and probable location in the Perseus spiral arm of the Galaxy , and these indicate a range in probable radius and mass of R / R _ { \odot } = 14 - 20 and M / M _ { \odot } = 16 - 35 , respectively .
These values are consistent with model evolutionary masses for single stars of this temperature and gravity .
Both stars are much smaller than their respective Roche radii , so the system is probably in a pre-contact stage of evolution .
A fit of the system ’ s spectral energy distribution yields a reddening of E ( B - V ) = 0.55 \pm 0.05 and a ratio of total-to-selective extinction of R = 2.97 \pm 0.15 .
We find no evidence of H \alpha emission from colliding stellar winds , which is probably the consequence of the low gas densities in the colliding winds zone .