31 Cygni

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31 Cygni
Cygnus constellation map.svg
Red circle.svg
Location of 31 Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension 20h 13m 37.907s[1]
Declination +46° 44′ 28.78″[1]
Apparent magnitude (V) 3.73 - 3.89[2]
Spectral type K4Iab + B4IV-V[2]
Variable type Algol[2]
Radial velocity (Rv)–7.41 ± 0.08[3] km/s
Proper motion (μ) RA: 4.78 ± 0.38[1] mas/yr
Dec.: 1.21 ± 0.35[1] mas/yr
Parallax (π)3.69 ± 0.41[1] mas
Distanceapprox. 880 ly
(approx. 270 pc)
Period (P)3786.1 ± 0.7 days
Eccentricity (e)0.224 ± 0.006
Periastron epoch (T)2,452,372.8 ± 2.2
Argument of periastron (ω)
206.4 ± 1.4°
Semi-amplitude (K1)
13.78 ± 0.13 km/s
K supergiant
Mass11.7 ± 1.3[4] M
Radius197 ± 20[4] R
Diameter197 ± 20[4] D
Luminosity4,300 ± 1,100[5] L
Temperature3,590 ± 225[5] K
B dwarf
Mass7.1 ± 0.8[4] M
Radius5.2 ± 0.5[4] R
[5] K
Other designations
ο1 Cyg, ο2 Cyg,[6] 31 Cyg, V695 Cyg, HD 192577, BD+46°2882, HIP 99675, HR 7735, SAO 49337
Database references
31 Cygni is the close pair. The third star is 30 Cygni.

31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, or V695 Cygni, is a star in the constellation Cygnus.

The Bayer designation ο (omicron) has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 31 Cygni has been designated, variously, as ο1 or ο2 Cygni — therefore for clarity, it is preferred to use the Flamsteed designation 31 Cygni.[6]

It is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The component stars are an orange supergiant of spectral type K4Iab and a blue-white star likely to be evolving off the main sequence with a spectral type of B4IV-V.

30 Cygni is another naked eye star a tenth of a degree away, forming a bright triple.

32 Cygni is about a degree away to the north, also a detached eclipsing binary system. It comprises a large cool evolved star and a small hot main sequence or subgiant companion.


  1. 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357. http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...474..653VFUL.Vizier catalog entry
  2. 2.0 2.1 2.2 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 Eaton, Joel A. et al. (2008). "Orbits and Pulsations of the Classical ζ Aurigae Binaries". The Astrophysical Journal 679 (2): 1490–1498. arXiv:0802.2238. Bibcode 2008ApJ...679.1490E. doi:10.1086/587452. http://iopscience.iop.org/0004-637X/679/2/1490/fulltext/.
  4. 4.0 4.1 4.2 4.3 Eaton, Joel A. (1993). "31 Cygni: The B star and the wind". Astronomical Journal 106: 2081. Bibcode 1993AJ....106.2081E. doi:10.1086/116787.
  5. 5.0 5.1 5.2 Di Benedetto, G. P.; Ferluga, S. (1990). "Angular diameters of Zeta Aurigae-type supergiants by Michelson interferometry". Astronomy and Astrophysics 236: 449. Bibcode 1990A&A...236..449D.
  6. 6.0 6.1 Kostjuk, N. D. (2004). "VizieR Online Data Catalog: HD-DM-GC-HR-HIP-Bayer-Flamsteed Cross Index (Kostjuk, 2002)". VizieR On-line Data Catalog: IV/27A. Originally published in: Institute of Astronomy of Russian Academy of Sciences (2002) 4027. Bibcode 2004yCat.4027....0K.

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