This large nebula is most often named GAL 025.4-00.2
or GAL 025.38-00.18
in the scientific literature. It has a bewildering number of different names in SIMBAD (not all cross-referenced).
It may be associated with the radio source W 42
It is visible in infrared
as the prominent bubble [CPA2006] N37
and appears to be ionised by an obscured O7 II giant.
The radio source W 42 has wildly varying distance estimates (from 13400 parsecs to 2200 parsecs). If the near estimate of 2200 parsecs (which is from a recent paper published in 2000
) is accepted, then W 42 is likely part of the Sh 2-60 nebula. Infrared imagery in the same paper shows that W 42 is energised by a massive, dense and young OB star cluster
embedded in an obscuring dust cloud in the bottom left part of this image.
To compound the confusion, the nebulosity in this direction actually consists of several distinct HII regions, one (G25.4SE) that has a distance estimated at 4600 parsecs (although the above paper identifies this as W 42 at 2200 parsecs) and another (G25.4NW) at a distance of about 12000 parsecs.[1
The average distance to the stars in this nebula is 2000 parsecs. [2
The distance to W 42 is only 2200 parsecs.[3
This is W 42.[4
Likely ionised by an O7 II giant. [5
The distant (14500 parsecs) radio source GAL 025.52+00.22
, is also in this field and is believed to house a Luminous Blue Variable similar to Eta Carinae.[6
1. ^ Lester, D. F., Dinerstein, H. L., Werner, M. W., et al. (1985). "Star
formation in the inner Galaxy - A far-infrared and radio study of two H II
regions", The Astrophysical Journal, Vol. 296, 565-575.
2. ^ Lahulla, J. F. (1985). "UBVRI photometry of stars in several H II
regions", Astronomy and Astrophysics Supplement Series, Vol. 61, 537-545.
3. ^ Blum, R. D., Conti, P. S., & Damineli, A. (2000). "The Stellar Content of
Obscured Galactic Giant H II Regions. II. W42", The Astronomical Journal,
Vol. 119, 1860-1871. [2000AJ....119.1860B]
4. ^ Woodward, C. E., Pipher, J. L., Helfer, H. L., et al. (1989). "G25.4-0.2S
- A Possible OB Cluster in the Inner Spiral Arm", Bulletin of the American
Astronomical Society, Vol. 21, 1155. [1989BAAS...21.1155W]
5. ^ Marco, A. & Negueruela, I. (2011). "An obscured cluster associated with
the H II region RCW173", Astronomy and Astrophysics, Vol. 534, A114.
6. ^ Clark, J. Simon, Steele, Iain A., & Langer, Norbert (2000). "Discovery of
a Bipolar Shell around G25.5+0.2", The Astrophysical Journal, Vol. 541,