2000ApJ...542..392Y

Near-infrared polarimetric images are presented for six molecular outflow sources: IRAS 20050+2720, IRAS 20126+4104, IRAS 20188+3928, S233, AFGL 5180, and AFGL 6366S. All the regions are found to exhibit reflection nebulae and to be associated with massive and clustered star formation. By inspecting polarimetric patterns in the nebulae, we have identified six deeply embedded sources (DESs) which illuminate circumstellar nebulosity but are not detectable in wavelengths shorter than 2 µm. While the DES in IRAS 20050 coincides with an infrared source in a previous, longer wavelength observation and the one in IRAS 20126 with a hot molecular core, the nature of the other newly discovered DESs is not known. From the compilation of the observations of DESs over a large wavelength range, we suspect that the DESs possess characteristics similar to hot molecular cores and are likely to be in the pre-ultracompact H II region phase of massive star formation.