Epoch J2000 Equinox J2000
|Right ascension||20h 32m 40.9589s|
|Declination||41° 14′ 29.286″|
|Apparent magnitude (B)||14.41|
|Apparent magnitude (V)||11.40|
|Apparent magnitude (J)||4.667±0.324|
|Apparent magnitude (H)||3.512±0.260|
|Apparent magnitude (K)||2.704±0.364|
|U−B color index||1.7|
|B−V color index||3.0|
|Proper motion (μ)||RA: 1.91 mas/yr
Dec.: −2.47 mas/yr
|Parallax (π)||0.60 ± 2.07 mas|
|Distance||approx. 10,000 ly
(approx. 2,000 pc)
|Absolute magnitude (MV)||−9.85|
Cygnus OB2 #12 is an extremely bright blue hypergiant with an absolute bolometric magnitude (all electromagnetic radiation) of −10.9, among the most luminous stars known in the galaxy. This makes the star nearly two million times more luminous than the sun, although less than half the estimates when the star was first discovered. It is now known to be a binary, with the companion approximately a tenth as bright. A very approximate initial estimate of the orbit gives the total system mass as 120M☉ and the period as 30 years.
It is a member of the Cyg OB2 Association, a cluster of young massive stars about 5000 light years away in Cygnus, and resides in a region of the Galaxy from which visible light is heavily absorbed by interstellar dust when viewed from the Earth. The dust causes the star to be strongly reddened despite being an intrinsically hot and blue star, hence it has been extensively studied in the infra-red. Were it not for the dust extinction, the star would have a visual magnitude about 1.5, nearly as bright as Deneb (Alpha Cygni), but because of the dust the observed visual magnitude is 11.4 so that it requires binoculars or a small telescope to be seen.
Cygnus OB2 #12 is a candidate luminous blue variable (LBV). Its position in the HR diagram, luminosity, and spectrum all classify it as an LBV, but it has not been observed to vary in brightness. The spectral type has varied slightly since its discovery, but not to the extent that would be normal for an LBV.
- Clark, J. S.; Najarro, F.; Negueruela, I.; Ritchie, B. W.; Urbaneja, M. A.; Howarth, I. D. (2012). "On the nature of the galactic early-B hypergiants". Astronomy & Astrophysics 541: A145. arXiv:1202.3991. Bibcode:2012A&A...541A.145C. doi:10.1051/0004-6361/201117472.
- De Jager, C. (1998). "The yellow hypergiants". Astronomy and Astrophysics Review 8 (3): 145–180. Bibcode:1998A&ARv...8..145D. doi:10.1007/s001590050009.
- Caballero-Nieves, Saida M.; Nelan, Edmund P.; Gies, Douglas R.; Wallace, Debra J.; Katherine DeGioia-Eastwood; Artemio Herrero; Wei-Chun Jao; Mason, Brian D. et al. (2013). "A High Angular Resolution Survey of Massive Stars in Cygnus OB2: Results from the Hubble Space Telescope Fine Guidance Sensors". arXiv:1311.5087v1 [astro-ph.SR].
- Online Astronomy: The Brightest Stars
- Tim Thompson: OB2-12
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