2006ApJ...639..975C

We have observed a high-mass protobinary system in the hot core W3(H₂O) with the BIMA array. Our continuum maps at wavelengths of 1.4 and 2.8 mm both achieve subarcsecond angular resolutions and show a double-peaked morphology. The angular separation of the two sources is 1".19, corresponding to 2.43x10³ AU at the source distance of 2.04 kpc. The flux densities of the two sources at 1.4 and 2.8 mm have a spectral index of 3, translating to an opacity law of κ_ν∝ν. The small spectral indices suggest that grain growth has begun in the hot core. We have also observed five K components of the methyl cyanide (CH₃CN) J=12⟶11 transitions. A radial velocity difference of 2.81±0.10 km/s is found toward the two continuum peaks. Interpreting these two sources as binary components in orbit about each other, we find a minimum mass of 22 M_☉for the system. Radiative transfer models are constructed to explain both the continuum and methyl cyanide line observations of each source. Power-law distributions of both density and temperature are derived. Density distributions close to the free-fall value, r^–1.5, are found for both components, suggesting continuing accretion. The derived luminosities suggest that the two sources have equivalent zero-age main-sequence (ZAMS) spectral type B0.5-B0. The nebular masses derived from the continuum observations are about 5 M_☉for source A and 4 M_☉ for source C. A velocity gradient previously detected may be explained by unresolved binary rotation with a small velocity difference.