2000A&A...357..637H

We present 450 and 850µm images of five ultracompact HII regions (G10.47, G12.21, G13.87, G31.41 and G43.89) taken at 9''/15'' resolution with SCUBA on the JCMT, and photometric measurements of the central sources at 1350 and 2000µm. We confirm that the sources have high submillimetre fluxes as expected from their IRAS fluxes at 100µm and molecular line emission. Each submillimetre image peaks towards the UCHII regions. Three sources (G10.47, G12.21 and G31.41) have particularly strong central peaks. These peaked sources, which can be easily identified from radial profiles, were previously identified from spectral line surveys as containing hot molecular cores. The non-peaked sources G13.87 and G43.89 do not have hot molecular cores. Using the DUSTY radiative transfer code, we model both the spectral energy distributions and radial profiles of the sources using a combination of r^–3/2 density profile envelopes plus, for the peaked sources, compact high optical depth cores. Although previous modelling of the SED of UCHII regions has been achieved with constant density shells, we find that r^–3/2 density profiles are necessary to fit the submm radial emission profiles of these sources. In agreement with previous modelling, we find that the inner radius of the dust shells is larger than would be expected from dust sublimation; the physical mechanism for this is unknown. Two sources (G10.47 and G12.21) have additional peaks within the 2.5' SCUBA field of view which are not known to contain UCHII regions and may contain high mass protostars.