Subarcsecond Imaging of the High-Mass Star Forming Region Onsala 1
  We report subarcsecond images of the high-mass star forming region Onsala 1
(ON 1) made with the Submillimeter Array (SMA) at 0.85 mm and the Very Large
Array at 1.3 cm and 3.6 cm. ON~1 is one of the smallest ultracompact HII
regions in the Galaxy and exhibits various star formation signposts. With our
VLA and SMA observations, two new cm-wave sources and five sub-mm dust sources,
respectively, within a field of ~3" (corresponding to a linear scale of 0.05
pc) are identified, indicating the multiplicity at the center of the ON 1
region. The dust and gas masses of these sub-mm sources are in the range of 0.8
to 6.4 M_sun. Among the five sub-mm dust sources, SMA2, with a dust and gas
mass of 2.6 M_sun, demonstrates several star formation signatures, and hence
likely represents an intermediate-mass (or even high-mass) star forming core.
Due to the low star formation efficiency of ~10%, we suggest that star
formation in the ON 1 region will continue. For example, SMA4 and SMA5 are not
associated with any star formation signatures and likely mark star formation
cores at very early evolutionary stages.
