GRS 305.40 +00.20 (Kes 18), often named simply G305, is a major star formation region associated with several HII regions, the star clusters Danks 1
and Danks 2
, an estimated 31 O stars and the Wolf-Rayet star WR 48a
. It may be one of the most massive star formation regions known in the Milky Way.
Avedisova finds three B-class ionising stars, including the B0.5 Iab supergiant HD 114122
and splits the objects in this direction across several star formation regions including SFR 305.25+0.20
and SFR 305.16-0.03
. However, Avedisova's information on this region is largely drawn from research published before the true nature of this region was revealed by the MSX and Spitzer infrared space telescopes and would not include the obscured core ionising clusters, which have not yet been properly analysed.
Dutra identifies the infrared star group [DBS2003] 82
and the infrared star clusters [DBS2003] 83
and [DBS2003] 84
in this direction. Although his notes state "not RCW 74" for the clusters, it is not clear what this means as the 3800 parsec distance estimate he gives places the clusters in the same direction and distance as the larger nebular complex.
You can see the full extent of the RCW 74 region in this spectacular Spitzer infrared image
"Consideration of the integrated radio flux of the complex implies that a minimum of 31 O7V stars must be present, under the assumption of no photon leakage. Given the age and morphology of the complex and in particular the observation that the central exciting clusters have entirely cleared their natal material, we expect this assumption will be violated, and hence that the true population of massive stars is likely to be significantly larger. If confirmed, the G305 complex represents one of the most massive regions of ongoing triggered star formation currently identified in the galaxy." [1
This is a major complex with many clusters, HII regions, a WR star and a giant molecular cloud. It appears to be part of a larger structure called the Centaurus Spur. [2
More details on the Centaurus Spur. [3
Dutra infrared cluster catalog. [4
1. ^ Clark, J. S. & Porter, J. M. (2004). "Triggered massive star formation in
the vicinity of WR 48a", Astronomy and Astrophysics, Vol. 427, 839-847.
2. ^ Danks, A. C., Wamsteker, W., Shaver, P. A., et al. (1984). "A
near-infrared study of the region L = 305 deg", Astronomy and Astrophysics,
Vol. 132, 301-311. [1984A&A...132..301D]
3. ^ Combi, J. A., Romero, G. E., & Arnal, E. M. (1998). "The spur-like radio
feature in Centaurus", Astronomy and Astrophysics, Vol. 333, 298-304.
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]