BC Cygni

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BC Cygni
Sadr Region rgb.jpg
Red circle.svg
BC Cygni is visible as a red star (circled). 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 38.55s
Declination 37° 31′ 58.9″
Apparent magnitude (V) 9.0 - 10.8[1]
Spectral type M3.5 Ia[2] (M2 - M5[3])
B−V color index +3.13 - +3.21[3]
Variable type SRc[2]
Distance1,230[3] pc
Absolute magnitude (MV)−7.71[4]
Mass19 M
Minimum (1900)
Radius1,553 R
Diameter1,553 D
Luminosity145,000 L
Temperature2,858 K
Maximum (2000)
Radius856 R
Luminosity112,000 L
Temperature3,614 K
Other designations
BC Cyg, HIP 100404, HV 3339, BD+37°3903, IRAS 20197+3722, 2MASS J20213855+3731589
Database references

BC Cygni (BC Cyg, HIP 100404, BD + 37 3903) is a red supergiant and pulsating variable star of spectral type M3.5Ia in the constellation Cygnus.

It is considered a member of the stellar Cygnus OB1 association, and within it the open cluster Berkeley 87.2 which would place at a distance of 1,500 parsecs (4,890 light-years) of the Solar System; however, according to the measure of the parallax by the satellite Hipparcos (1.20 milliarcseconds). It is less than a degree north of another variable red supergiant, BI Cygni.

BC Cygni was calculated to have an effective temperature of 2,858 to 3,614 K and to vary between 112,000 to 145,000 L. The size at its brightest and coolest has been calculated to be 1,553 D compared to 856 D at the hottest and faintest. It is one of largest stars known. If it were in the place of the Sun, its photosphere would engulf the orbit of Jupiter assuming the maximum radius of 1,553 D. With a mass of about 19 M, it is estimated that the stellar mass loss, as dust, as the atomic and molecular gas could not be evaluators is 3.2×10−9 M per year. This mass is an indication that this star will end up exploding as a supernova.

The brightness of BC Cyg varies from visual magnitude +9.0 and +10.8 with a period of 720 ± 40 days.[1] Between 1,900 and 2,000 appears to have increased its average brightness of 0.5 magnitudes.[3]

See also[edit]


  1. 1.0 1.1 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.
  2. 2.0 2.1 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 3.3 3.4 Turner, David G.; Rohanizadegan, Mina; Berdnikov, Leonid N.; Pastukhova, Elena N. (2006). "The Long-Term Behavior of the Semiregular M Supergiant Variable BC Cygni". The Publications of the Astronomical Society of the Pacific 118 (849): 1533. Bibcode 2006PASP..118.1533T. doi:10.1086/508905.
  4. Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.

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