BD+40° 4210 is a hot luminous giant star located in the constellation Cygnus. It is a member of the Cygnus OB2 association and a candidate Luminous Blue Variable.

BD+40° 4210
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension  20h 31m 04.659s[1]
Declination +40° 30′ 56.93″[1]
Apparent magnitude (V) 10.45[2]
Spectral type B1III:e[1]
Apparent magnitude (K) 4.466[3]
Apparent magnitude (J) 5.469[3]
Apparent magnitude (H) 4.833[3]
B−V color index 1.68[2]
Variable type candidate cLBV[1]
Proper motion (μ) RA: −3.1731±0.097[4] mas/yr
Dec.: −4.612±0.114[4] mas/yr
Parallax (π)0.6530 ± 0.0568[4] mas
Distance5,000 ± 400 ly
(1,500 ± 100 pc)
Absolute magnitude (MV)-7.66[1]
Mass54[1] M
Radius55.9[citation needed] R
Luminosity (bolometric)630,000[5] L
Temperature21,353[1] K
Age3.5[1] Myr
Other designations
BD+40° 4210, IRAS 20292+4020, 2MASS J20310464+4030568, TYC 3157-679-1, PPM 60064
Database references


BD+40° 4210 is heavily reddened and extinguished by the interstellar dust of the Milky Way and little studied. It has turned out to be one of the most luminous stars of the Cygnus OB2 association, with an absolute magnitude of -7.66 and a bolometric luminosity more than 600,000 times that of our Sun. It has been assigned a B1III spectral classification, but with peculiarities including unusually shallow lines and broad emission. Despite the giant luminosity class, the luminosity appears to be extremely high, placing it on or near the S Doradus instability strip occupied by quiescent luminous blue variables. Its brightness varies by less than 0.1 magnitudes on a timescale around 100 days.[1]

BD+40° 4210 is located at a projected 4.8 parsecs from the candidate luminous blue variable G79.29+0.46 and probably at a similar distance since both are assumed members of Cygnus OB2; however, unlike the latter which is surrounded by an extensive ring-shaped nebulosity, no nebula has been found around this star.[1]


  1. ^ a b c d e f g h i j Comerón, F.; Pasquali, A. (2012). "New members of the massive stellar population in Cygnus". Astronomy & Astrophysics. 110: 2715. Bibcode:2012A&A...543A.101C. doi:10.1051/0004-6361/201219022.
  2. ^ a b Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862.
  3. ^ a b c Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C. 2246: 0. Bibcode:2003yCat.2246....0C.
  4. ^ a b c Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ Archived 2016-03-03 at the Wayback Machine In and around the rich association Cygnus OB2