Abstract
W3(OH) is an ultracompact HII region in the Perseus arm at a distance of 2.04 kpc. In its vicinity, W3(H2O) is a hot molecular core located just 6′′, or 0.06 pc, to the east of W3(OH). Past single–element telescope studies showed that many molecular lines were detected toward these regions, and suggested the presence of a hot molecular core in W3(H2O). Interferometric observations at high angular resolutions later suggested a dichotomy between the oxygen-containing molecules and the nitrogen-containing species in W3(H2O) and W3(OH). In this study, we carry out interferometric observations at submillimeter wavelengths with the SMA at nearly subarcsecondresolution to investigate W3(H2O), W3(OH), and their surroundings. Our observations show that W3(H2O) is dominated by the thermal dust emission at 850 μm and the hydrogen column density NH2 is about 7.88×1023 cm−2 toward this source. W3(OH) is, however, dominated by free–free emission even at this submillimeter wavelength and the upper limit of NH2 is about 1023 cm−2. From the detected methanol transitions, we estimated the gas temperature to be about 189 K in W3(H2O), and 93 K in W3(OH). The derived molecular fractional abundances show in general agreement with, but cannot confirm the chemical differentiation between N/O-containing molecules in W3(H2O)/W3(OH) that was proposed by Wyrowski et al. (1999).