According to a 1975 paper, RCW 99 is an extended HII region with low density and 102 solar masses of gas and dust.
Avedisova lists 5 ionising stars, including the hot O5 III giant LSS 3443
, the O9.5 II giant CP -53 6950
and 3 B-class supergiants. She places the nebula in star formation region SFR 328.60-0.51
along with the star cluster Trumpler 23
The Georgelins give an O7 III class for LSS 3443 and SIMBAD lists it as a B-class star. A 2006 paper gives an age of 700 milion years and a distance of 2200 parsecs for Trumpler 23, raising some doubts as to whether this cluster can really be associated with RCW 99.
Dutra says that the infrared cluster [DBS2003] 98
is deeply embedded in RCW 99.
RCW 99 is an intensely bright infrared source as can be seen in this Spitzer image
Trumpler 23 has an age of 700 million years and a distance of 2200 parsecs.[1
This is an extended HII region with low density and 102 solar masses.[2
Dutra says that the infrared cluster [DBS2003] 98 is deeply embedded in RCW 99. [3
Pinheiro et.al. claim in a 2010 paper that "No hot star towards [RCW 99] had been previously identified." and list O7 III and B2 V class ionising stars, [4
] These appear to be identical to two of the ionising stars listed by Avedisova in 1984.
1. ^ Carraro, G., Janes, K. A., Costa, E., et al. (2006). "Photometry of seven
overlooked open clusters in the first and fourth Galactic quadrants",
Monthly Notices of the Royal Astronomical Society, Vol. 368, 1078-1086.
2. ^ Braz, M. A., Jardim, J. O., & Kaufmann, P. (1975). "Characteristics of
planetary nebulae and H II regions based on lambda equals 1.35 CM continuum
measurements", Astronomy and Astrophysics, Vol. 43, 153-155.
3. ^ 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]
4. ^ Pinheiro, M. C., Copetti, M. V. F., & Oliveira, V. A. (2010). "Spectral
classification and distance determination of stars in nine southern
Galactic H II regions", Astronomy and Astrophysics, Vol. 521, A26.