NGC 2404

NGC 2404 is a massive H II region inside NGC 2403, a spiral galaxy in Camelopardalis. It was discovered on February 2, 1886 by Gulliaume Bigourdan. NGC 2404 is approximately 940 ly in diameter, making it one of the largest H II regions so far known. It is the largest H II region in NGC 2403, and lies at the outskirts of the galaxy, making for a striking similarity with NGC 604 in M33, both in size and location in the host galaxy. This H II region contains 30-40 Wolf-Rayet stars,[5] and unlike the Tarantula Nebula, but similar to NGC 604, NGC 2404's open cluster is probably much less compact, so it probably looks like a large stellar association. This H II region is probably only a few million years old.

NGC 2404
Emission nebula
H II region
NGC 2404 is the giant H II region to the left
Observation data: J2000 epoch
Right ascension07h 36m 51.4s[1]
Declination+65° 36′ 09″[1]
Distance9,650,000 ly   (2,960,000[2] pc)
Apparent magnitude (V)+16.9
Apparent dimensions (V)20 arcsecs[3]
ConstellationCamelopardalis
Physical characteristics
Radius470 (estimated)[4] ly
Absolute magnitude (V)-14.5
Notable featuresMassive H II region,
the largest one in NGC 2403.

References
  1. "NASA/IPAC Extragalactic Database". Results for NGC 2403. Retrieved 2006-11-21.
  2. Carlin, Jeffrey L.; Garling, Christopher T.; Peter, Annika H. G.; Crnojević, Denija; Forbes, Duncan A.; Hargis, Jonathan R.; Mutlu-Pakdil, Burçin; Pucha, Ragadeepika; Romanowsky, Aaron J.; Sand, David J.; Spekkens, Kristine; Strader, Jay; Willman, Beth (2019). "Tidal Destruction in a Low-mass Galaxy Environment: The Discovery of Tidal Tails around DDO 44". The Astrophysical Journal. 886 (2): 109. arXiv:1906.08260. Bibcode:2019ApJ...886..109C. doi:10.3847/1538-4357/ab4c32. S2CID 195218404.
  3. http://library.navoiy-uni.uz/files/O'Meara%20C.%20O.%20-%20The%20Caldwell%20Objects%20(1st%20edition)(2002)(484s).pdf
  4. distance × sin( diameter_angle / 2 ) = 470 ly. radius
  5. Finlay, W. H. (April 18, 2006). Concise Catalog of Deep-sky Objects: Astrophysical Information for 500 Galaxies, Clusters and Nebulae. Springer Science & Business Media. ISBN 9781852338510 – via Google Books.
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