BI Cygni

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 is considered a member of the stellar Cygnus OB1 association,[4] its distance is around 1,400 parsecs (4,500 light-years) of the Solar System. It is less than a degree south of another variable red supergiant, BC Cygni.

BI Cygni
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]
Characteristics
Spectral type M4 Iab[2]
Variable type Lc[2]
Astrometry
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
Distanceapprox. 4,500 ly
(approx. 1,400 pc)
Absolute magnitude (MV)−6.78[4]
Details
Mass6.3[5] M☉
Radius666[6] R☉
Luminosity64,000 - 67,000[6] L☉
Surface gravity (log g)-0.35[5] cgs
Temperature3,550±170[6] K
Metallicity [Fe/H]+0.40[5] dex
2016 (maximum)
Radius908+12
−10[7] R☉
2015 (minimum)
Radius852+12
−9[7] R☉
Other designations
BI Cygni, BD+36 4025, IRC+40408, 2MASS J20212192+3655555, IRAS 20194+3646, WDS J20214+3656, AAVSO 2017+36B
Database references
SIMBADdata

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.[8]

BI Cyg is one of the largest known stars with a radius around 1,240 R☉ based on the assumption of an effective temperature of 3,575 K and a bolometric luminosity of 226,000 L☉.[4] More recent studies derive lower luminosities below 150,000 L☉, suggesting an initial mass of 20 M☉, and consequently lower values for the radius.[9][10][6]

See also

References
  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. Samus, N. N.; Durlevich, O. V.; et al. (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. 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.
  4. 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.
  5. Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; De Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765.
  6. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd.
  7. Norris, Ryan P. (2019). Seeing Stars Like Never Before: A Long-term Interferometric Imaging Survey of Red Supergiants (PDF) (PhD). Georgia State University.
  8. 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): 1721–1734. arXiv:astro-ph/0608438. Bibcode:2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x.
  9. 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.
  10. 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.
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