BI Cygni

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BI Cygni
Sadr Region rgb.jpg
Red circle.svg
BI Cygni is the small very red dot right on the left edge of this image. The bright star at the centre is γ Cygni and north is to the right.
Credit: Erik Larsen
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 21m 21.8803s[1]
Declination 36° 55′ 55.771″[1]
Apparent magnitude (V) 8.4 - 9.9[2]
Spectral type M4 Iab[2]
Variable type Lc[2]
Proper motion (μ) RA: −2.929±0.140[3] mas/yr
Dec.: −5.223±0.151[3] mas/yr
Parallax (π)0.7269 ± 0.0811[3] mas
Distance1,580[4] pc
Absolute magnitude (MV)−6.78[5]
Radius850[6] - 1,240[5] R
Diameter850[6] - 1,240[5] D
Luminosity123,000[4]-226,000[5] L
Temperature3,575[5][4]-3,720[6] K
Database references

BI Cygni (BI Cyg, IRC +40408, BD+36 4025) is a red supergiant in the constellation Cygnus. It is an irregular variable star with a maximum brightness of magnitude 8.4 and a minimum of magnitude 9.9. It has a current mass of 20 M.[6]

It is considered a member of the stellar Cygnus OB1 association,[5] its distance is 1,580 parsecs (5,150 light-years) of the Solar System. It is less than a degree south of another variable red supergiant, BC Cygni.

BI Cyg is a slow irregular variable star classified as type Lc, an irregular supergiant. Its brightness changes between extremes of magnitude 8.4 and 9.9.[2] Frequency analysis of its light curve shows no significant periods.[7]

BI Cyg is one of largest known stars with a radius around 1,240 D based on the assumption of an effective temperature of 3,575 K and a bolometric luminosity of 226,000 L.[5] More recent studies derive lower luminosities below 130,000 L, suggesting an initial mass of 20 M, and consequently lower values for the radius.[4][6]

See also


  1. 1.0 1.1 Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics 335: L65. Bibcode 1998A&A...335L..65H.
  2. 2.0 2.1 2.2 2.3 Samus, N. N.Expression error: Unrecognized word "etal". (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S 1. Bibcode 2009yCat....102025S.
  3. 3.0 3.1 3.2 Brown, A. G. A. (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.
  4. 4.0 4.1 4.2 4.3 Nicolas Mauron; Eric Josselin (2010). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics 526: A156. arXiv:1010.5369. Bibcode 2011A&A...526A.156M. doi:10.1051/0004-6361/201013993.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 Table 4 in Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (August 2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought". The Astrophysical Journal 628 (2): 973–985. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.
  6. 6.0 6.1 6.2 6.3 Josselin, E.; Plez, B. (2007). "Atmospheric dynamics and the mass loss process in red supergiant stars". Astronomy and Astrophysics 469 (2): 671–680. arXiv:0705.0266. Bibcode 2007A&A...469..671J. doi:10.1051/0004-6361:20066353.
  7. Kiss, L. L; Szabó, Gy. M; Bedding, T. R (2006). "Variability in red supergiant stars: Pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society 372 (4): 1721. arXiv:astro-ph/0608438. Bibcode 2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x.

External links