654 GHz Continuum and C 18 O(6-5) Observations of G240.31+0.07 with the Submillimeter Array

We report a dual-band observation at 223 and 654 GHz (460 micron) toward anultracompact (UC) HII region, G240.31+0.07, with the Submillimeter Array. Witha beam size of 1"5 X 0"8, the dust continuum emission is resolved into twoclumps, with clump A coincident well with an H2O maser and the UC HII region.The newly discovered clump, B, about 1"3 (~8.3 X 10^3 AU) to the southwest ofclump A, is also associated with H2O masers and may be a more recentstar-forming site. The continuum flux densities imply an opacity spectral indexof \beta = 1.5 +- 0.3, suggestive of a value lower than the canonical 2.0 foundin 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 inthe 223 GHz band. A radial velocity difference of 2.5 +- 0.4 km/s is foundbetween the two clumps in C18O (6-5) emission. The total (nebular and stellar)mass of roughly 58 Msun in the central region is close to, but not by farlarger than, the minimum mass required for the two clumps to be gravitationallybound for binary rotation. Our continuum data do not suggest a large amount ofmatter associated with the H2 knots that were previously proposed to arise froma massive disk or envelope.Comment: 12 pages, 2 tables, 3 figures, accepted by the Astrophysical Journal Letter