A high-mass protobinary system in the hot core W3(H2O).
CHEN H.-R., WELCH W.J., WILNER D.J. and SUTTON E.C.
Abstract (from CDS):
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 κν∝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.