Avedisova says that this nebula is ionised by the O9.5 V star HD 158186
and the B2 V Antalova OB-51
. She places it in star formation region SFR 355.89+1.61
along with the star cluster Antalova 1
. It is next to the larger Sh 2-12 (part of which is on the lower left of this image).
Kharchenko's cluster database
includes Antalova 1 with HD 158186 as a member. However, she gives a significantly cooler B2/B3II class for HD 158186 and a much closer distance of 850 parsecs.
Kharchenko gives a distance of 850 pc [1
] and a mass of 137 solar masses [2
] for Antalova 1.
It is not clear whether HD 158186 is a member of Antalova 1 as one paper states that this star may be a runaway star ejected from NGC 6383, the cluster that ionises Sh 2-12. [3
The nebula can be seen here
and Sh 2-11, Sh 2-12 and Sh 2-13 can be seen together in this hydrogen-alpha image.
1. ^ Kharchenko, N. V., Piskunov, A. E., Röser, S., et al. (2005).
"Astrophysical parameters of Galactic open clusters", Astronomy and
Astrophysics, Vol. 438, 1163-1173. [2005A&A...438.1163K]
2. ^ Piskunov, A. E., Schilbach, E., Kharchenko, N. V., et al. (2008). "Tidal
radii and masses of open clusters", Astronomy and Astrophysics, Vol. 477,
3. ^ de Wit, W. J., Testi, L., Palla, F., et al. (2005). "The origin of massive
O-type field stars: II. Field O stars as runaways", Astronomy and
Astrophysics, Vol. 437, 247-255. [2005A&A...437..247D]