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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 ± 0.0002 days) and made Doppler tomographic reconstructions of the component spectra. A comparison of these with model spectra from non-LTE, line-blanketed atmospheres indicates that the two stars have almost identical masses (M2/M1 = 1.020 ± 0.014), temperatures (Teff = 28,000 ± 1000 K), gravities (log g = 3.25 ± 0.25), and projected rotational velocities (V sin i ≲ 30 km s-1). We investigate a number of constraints on the radii and masses of the stars based on 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⊙ = 14-20 and M/M⊙ = 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 precontact stage of evolution. A fit of the system's spectral energy distribution yields a reddening of E(B - V) = 0.55 ± 0.05 and a ratio of total-to-selective extinction of R = 2.97 ± 0.15. We find no evidence of Hα emission from colliding stellar winds, which is probably the consequence of the low gas densities in the colliding winds zone. © 2006. The American Astronomical Society. All rights reserved.

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Astrophysical Journal

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