This HII region is ionised by the young NGC 6604
star cluster, which includes the O5-8V+O5-8V+O8I supergiant multiple HD 167971
and the radio source W 35
. It lies, unusually, about 70 parsecs above the galactic plane within the Ser OB2
Ser OB2 contains over 100 OB stars with a common age of about 5 million years.
A good image of this nebula, which looks like a nest (Gum 84) carrying a tiny egg (Gum 85), can be seen here
Sh 2-54 is associated with Ser OB2 at a distance of 1900 pc. Ser OB2 contains more than 100 OB stars with a common age of about 5 million years. It is located about 70 pc above the galactic plane.[1
The young NGC 6604 cluster contains the multiple HD 167971 (O5-8V+O5-8V+(O8I)) [2
The nebula is prominent at infrared frequencies as can be seen in this MSX image
Avedisova places Sh 2-54 in the star formation region SFR 18.68+1.97
along with three masers, the young stellar object IRAS 18151-1208
, and the Wolf-Rayet star WR 113
Sharpless describes a large region, so this nebula would be the large nebula, not just the small bright one within.
The nebula contains the infrared cluster [BDS2003] 9
, which appears to ionise the tiny Gum 85 "egg" that appears within the larger Sh 2-54 "nest". The Bica et.al. catalog gives a distance estimate of 2600 parsecs for the infrared cluster, so it may be further away than Sh 2-54 itself. [3
According to Marsalkova, RCW 167 = Sh 2-54 = Gum 84-85, however Gum states that Gum 85 "Almost lies within [Gum] 84 but this is probably a case of alignment ... They are probably separate objects."
1. ^ Forbes, Douglas (2000). "The Serpens OB2 Association and Its Thermal
``Chimney''", The Astronomical Journal, Vol. 120, 2594-2608.
2. ^ De Becker, M., Rauw, G., Blomme, R., et al. (2005). "An XMM-Newton
observation of the multiple system HD 167971 (O5-8V + O5-8V + (O8I)) and
the young open cluster NGC 6604", Astronomy and Astrophysics, Vol. 437,
3. ^ Bica, E., Dutra, C. M., Soares, J., et al. (2003). "New infrared star
clusters in the Northern and Equatorial Milky Way with 2MASS", Astronomy
and Astrophysics, Vol. 404, 223-232. [2003A&A...404..223B]