This is the HII region NGC 2579, which is ionised by three O-class stars. A 1998 paper argues that it is associated with RCW 19. However, a more recent 2007 paper gives a much greater distance for NGC 2579, placing it in the Norma arm.
According to a 2007 paper, NGC 2579 has a distance of 7600 +/- 900 pc and is ionised by three O-class stars: DENIS-P J082052.8-361258 / VdBH 13a B
(O5 V), DENIS-P J082054.8-361258 / VdBH 13b A
(O6.5 V) and DENIS-P J082055.0-361306 / VdBH 13b B
(O8 V). [1
The same paper states that Gum 11 = NGC 2579 is an HII region and is *not* RCW 20 - they are completely different objects. The paper gives no reason for making this distinction and it is an odd statement to make because the RCW catalog itself identifies RCW 20 with both Gum 11 and NGC 2579 and clearly identifies a nebula with the same extent and location. As Gum's coordinates are not completely accurate, the fact that the location he gives is slightly different is no evidence for distinguishing these objects.
Moffat, Fitzgerald and Jackson (1979) identified 7 possible ionising stars in the direction of RCW 20. They give only spectral types for 3 B-class stars. [2
This is in the same location as the reflection nebula NGC 2579 (Gum 11).[3
RCW 19/20 have a joint distance of 3400 pc.[4
1. ^ Copetti, M. V. F., Oliveira, V. A., Riffel, R., et al. (2007). "A study of
the neglected Galactic H ii region NGC 2579 and its companion ESO 370-9",
Astronomy and Astrophysics, Vol. 472, 847-854. [2007A&A...472..847C]
2. ^ Moffat, A. F. J., Jackson, P. D., & Fitzgerald, M. P. (1979). "The
rotation and structure of the galaxy beyond the solar circle. I -
Photometry and spectroscopy of 276 stars in 45 H II regions and other young
stellar groups toward the galactic anticentre", Astronomy and Astrophysics
Supplement Series, Vol. 38, 197-225. [1979A&AS...38..197M]
3. ^ Bhatt, H. C., Jain, S. K., & Sagar, R. (1998). "The Puppis OB III
association: polarization measurements", Astronomy and Astrophysics, Vol.
331, 737-741. [1998A&A...331..737B]
4. ^ Neckel, Th. & Staude, H. J. (1995). "IRAS 08159-3543: Optical Detection of
the Dusty, Neutral Bipolar Wind of a Luminous Young Stellar Object", The
Astrophysical Journal, Vol. 448, 832. [1995ApJ...448..832N]