Avedisova adds 4 B-class ionising stars.
A Chandra X-ray study finds 304 X-ray sources and gives an age estimate of only 300 thousand years. [1
SIMBAD gives a class of O6 for HD 164492 but a 2011 paper gives a O7.5 class for this star. [2
There is a surprising range of distance estimates for the Trifid nebula.
Analysis based on the velocity of gas measured in the Trifid direction using radio telescopes suggests that the Trifid nebula lies at a distance of 3010 parsecs. [3
A visual examination of the A component of HD 164492 suggests a distance of 1680 parsecs. [4
Including the other B-F components of HD 164492 suggests a distance of between 2500 to 2800 parsecs according to a 1999 paper [5
] and this uncertainty range is extended by a 2011 paper examining the dust extinction observed towards the nebula and concluding a distance range of 2700 +/- 500 parsecs. [6
But a study of NGC 6514, the star cluster that includes HD 164492, concludes that the Trifid nebula is much closer than any of these other estimates - only 816 parsecs
1. ^ Rho, Jeonghee, Ramírez, Solange V., Corcoran, Michael F., et al. (2004).
"Chandra Observation of the Trifid Nebula: X-Ray Emission from the O Star
Complex and Actively Forming Pre-Main-Sequence Stars", The Astrophysical
Journal, Vol. 607, 904-912. [2004ApJ...607..904R]
2. ^ Torii, K., Enokiya, R., Sano, H., et al. (2011). "Molecular Clouds in the
Trifid Nebula M20: Possible Evidence for a Cloud-Cloud Collision in
Triggering the Formation of the First Generation Stars", The Astrophysical
Journal, Vol. 738, 46. [2011ApJ...738...46T]
3. ^ Paladini, R., Burigana, C., Davies, R. D., et al. (2003). "A radio catalog
of Galactic HII regions for applications from decimeter to millimeter
wavelengths", Astronomy and Astrophysics, Vol. 397, 213-226.
4. ^ Lynds, B. T., Canzian, B. J., & Oneil, E. J., Jr. (1985). "Optical
measurements of the Trifid dust", The Astrophysical Journal, Vol. 288,
5. ^ Kohoutek, L., Mayer, P., & Lorenz, R. (1999). "Photometry and spectroscopy
of the central star of the Trifid nebula", Astronomy and Astrophysics
Supplement Series, Vol. 134, 129-133. [1999A&AS..134..129K]
6. ^ Cambrésy, L., Rho, J., Marshall, D. J., et al. (2011). "Variation of the
extinction law in the Trifid nebula", Astronomy and Astrophysics, Vol.
527, A141. [2011A&A...527A.141C]
7. ^ 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]