RCW 121, RCW 122 and RCW 123 are probably ionised by stars in the Havlen-Moffat 1
cluster. There is a large and very uncertain range of distance estimates for the objects in this direction, from 2000 to 5000 parsecs.
A 2012 study used radio parallax to determine the distance to a maser in the direction of RCW 122 as 3380 parsecs, strongly implying that this is the distance of the entire Havlen-Moffat 1 star formation region.
RCW 122 separates into at least two distinct sources in infrared. The brightest one by far is IRAS 17167-3854
, which is sometimes further subdivided into RCW 122A
and RCW 122B
. Dutra and colleagues locate the infrared cluster [DBS2003] 119
in this direction at 2000 parsecs. A distinct smaller nebula to the northwest in galactic coordinates is IRAS 17158-3901
, also known as RCW 122C
. These sources are ionised by several O-stars, including one as bright as O4.
A 2008 paper concludes that RCW 121 and RCW 122 are embedded in a 1.2 million solar mass molecular cloud and both nebulae are likely ionised by several O7 V class stars.
The larger region around RCW 121, RCW 122 and RCW 123 is spectacular in infrared. This Spitzer image shows only a part of this region.
While not as detailed, this MSX image
shows a wider view of the region in which the compact HII regions RCW 121 and 122 are seen to be bright knots at the rim of a vast star forming cavity centred on the ionising cluster Havlen-Moffat 1 and filled by the diffuse HII region RCW 123.
RCW 121 and RCW 122 are embedded in a 1.2 million solar mass molecular cloud and both nebulae are likely ionised by several O7 V class stars with a distance of about 5000 parsecs.[1
RCW 122 and RCW 123 are probably ionised by stars in the Havlen-Moffat No. 1 cluster.[2
The massive star formation region RCW 122 is ionised by several O-stars, including one as bright as O4.[3
Dutra et.al. infrared star cluster catalog. [4
1. ^ Arnal, E. M., Duronea, N. U., & Testori, J. C. (2008). "Molecular gas
associated with RCW 121 and RCW 122", Astronomy and Astrophysics, Vol.
486, 807-818. [2008A&A...486..807A]
2. ^ Vázquez, R. A. & Baume, G. (2001). "The open cluster Havlen-Moffat No. 1
revisited", Astronomy and Astrophysics, Vol. 371, 908-920.
3. ^ Ghosh, S. K., Iyengar, K. V. K., Rengarajan, T. N., et al. (1989).
"Far-infrared (120-300 micron) observations of southern H II regions", The
Astrophysical Journal Supplement Series, Vol. 69, 233-239.
4. ^ Dutra, C. M., Bica, E., Soares, J., et al. (2003). "New infrared star
clusters in the southern Milky Way with 2MASS", Astronomy and Astrophysics,
Vol. 400, 533-539. [2003A&A...400..533D]