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C. Watson, E. Churchwell (U. Wisconsin-Madison), T. R. Hunter (CfA), Pierre Cox (U. Paris)
We present 350 \mum continuum images of 23 massive star formation regions obtained with the Caltech Submillimeter Observatory equipped with the SHARC focal plane array. The 350 \mum emission is compared with thermal radio continuum emission and OH, H2O, and CH3OH masers.
Emission at 350\mum is believed to be thermal emission from dust heated by embedded or nearby stars. Compact radio continuum sources are usually present in the mapped 350 \mum fields which lends strong support to the notion that the dust is heated primarily by hot stars. Masers, which are also a common property of massive star formation regions, are also shown frequently close to the 350 \mum peaks. It is postulated that those 350 \mum sources without radio continuum counterparts may be undergoing such rapid accretion that the in-falling matter quenches the HII region very close to the protostar thereby making the HII region undetectable in free-free emission. Objects in this evolutionary state may well represent the long sought after precursors to UC HII regions and should have the properties of accreting massive protostars (i.e. accretion disks, bipolar molecular outflows, hot shocked gas, in-fall with spin-up toward the protostar, etc.). We suggest that the ten sources in this category in our sample merit further observational study for these properties.