You can see the full extent of this huge nebula in this hydrogen-alpha SuperCOSMOS image
The bubble surrounding HD 153919 is discussed by Benaglia and Cappa. [1
HD 153919 is a runaway star ejected from the Sco OB1 association in a supernova explosion about 2 million years ago.[2
Avedisova lists a second ionising star for RCW 119 (the O9 II-III class HD 153426
). SIMBAD says that this is associated with the separate HII region Gum 57a.
A 2004 paper concludes that HD 153426 is part of an uncatalogued star cluster at distance of 2100 parsecs.[3
The RCW catalog uses RCW 119 to designate the entire emission region surrounding HD 153919 and RCW 119a for the enhanced emission seen in the direction of HD 153426. Similarly, Gum uses Gum 57a to designate the enhanced emission and Gum 57b to designate the full HD 153919 emission region.
The Piskunov et.al. cluster catalog gives a distance of 494 pc and an age of about 350 million years for NGC 6281. [4
] This would place this cluster between the Orion spur and the Sagittarius arm. It is common to find older clusters outside the major spiral structures as over hundreds of millions of years they can drift from their birthplaces.
SIMBAD lists the hottest star in NGC 6281 as B8 so there can't be much ionising caused directly by the cluster. Most of this must be from hotter background stars.
1. ^ Benaglia, P. & Cappa, C. E. (1999). "Possible wind blown bubbles
associated with five Of stars", Astronomy and Astrophysics, Vol. 346,
2. ^ Ankay, A., Kaper, L., de Bruijne, J. H. J., et al. (2001). "The origin of
the runaway high-mass X-ray binary HD 153919/4U1700-37", Astronomy and
Astrophysics, Vol. 370, 170-175. [2001A&A...370..170A]
3. ^ de Wit, W. J., Testi, L., Palla, F., et al. (2004). "The origin of massive
O-type field stars. I. A search for clusters", Astronomy and Astrophysics,
Vol. 425, 937-948. [2004A&A...425..937D]
4. ^ Piskunov, A. E., Schilbach, E., Kharchenko, N. V., et al. (2008). "Tidal
radii and masses of open clusters", Astronomy and Astrophysics, Vol. 477,