Klaus W. Hodapp
Institute for Astronomy, University of Hawaii
Nicola Schneider
IRFU/SAp CEA/DSM, Lab. AIM CNRS, 91191 Gif-sur-Yvette, France
To appear in Handbook of Star Forming Regions
S106 is a bipolar nebula illuminated and excited by a central star called
S106 IR. Depending on its distance (literature values range from 500 pc to 5.7 kpc) this
is a late O to early B star. There is evidence that S106 is physically associated with the
molecular cloud complex of Cygnus X. The bipolar nebula is the dominant feature in an
embedded cluster of young stars forming in a molecular cloud. The bipolar morphology
is visible from optical wavelengths into radio wavelengths, implying that it is not caused
by foreground extinction. Instead, it is caused by the shadowing effect of a small disk
surrounding the exciting star that projects into the surrounding molecular cloud and
confines ionizing radiation to the lobes. With the discovery of new star formation sites
in S106, i.e. YSOs in the S106 cluster, additional sub-clusters, the Class 0 source S106
FIR, and dense cold cores as reservoirs for new stars, S106 can nowadays be seen as
a region of active star formation. This view revises earlier interpretations of radio and
molecular line observations that saw S106 IR as a single massive protostar with a large
accretion disk.