2007ApJ...654L..87C

We report a dual-band observation at 223 and 654 GHz (460 µm) toward an ultracompact (UC) H II region, G240.31+0.07, using the Submillimeter Array. With a beam size of 1.5"x0.8", the dust continuum emission is resolved into two clumps, with clump A well coincident with an H₂O maser and the UC H II region. The newly discovered clump, B, about 1.3" (≃8.3x10³ AU) to the southwest of clump A, is also associated with H₂O masers and may be a more recent star-forming site. The continuum flux densities imply an opacity spectral index of β=1.5±0.3, suggestive of a value lower than the canonical 2.0 found in the interstellar medium and in cold, massive cores. The presence of hot (≃100 K) molecular gas is derived by the brightness ratio of two H₂CO lines in the 223 GHz band. A radial velocity difference of 2.5±0.4 km/s is found between the two clumps in C¹⁸O(6-5) emission. The total (nebular and stellar) mass of roughly 58 M_☉in the central region is close to, but not much larger than, the minimum mass required for the two clumps to be gravitationally bound for binary rotation. Our continuum data do not suggest a large amount of matter associated with the H₂knots that were previously proposed to arise from a massive disk or envelope.