32 Cygni

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32 Cygni
Cygnus constellation map.svg
Red circle.svg
Location of 32 Cygni (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 15m 28.32289s[1]
Declination +47° 42′ 51.1609″[1]
Apparent magnitude (V) 3.98[2] (3.90 - 4.14[3])
Spectral type K5 Iab + B7 V[4]
U−B color index +1.03[2]
B−V color index +1.52[2]
Variable type EA[3]
Radial velocity (Rv)-14.4[5] km/s
Proper motion (μ) RA: +5.30[1] mas/yr
Dec.: +2.33[1] mas/yr
Parallax (π)3.08 ± 0.6[1] mas
Distanceapprox. 1,100 ly
(approx. 320 pc)
Period (P)1,147.8 days
Semi-major axis (a)5.50 ± 1.20 mas
Eccentricity (e)0.300
Inclination (i)65.50 ± 8.30°
Periastron epoch (T)2433141.8 HJD
Argument of periastron (ω)
32 Cyg A
Mass7.45[7] M
Radius184[7] R
Diameter184[7] D
Luminosity6,600[7] L
Surface gravity (log g)0.78[7] cgs
Temperature3,840[7] K
Metallicity [Fe/H]–0.43[8] dex
Age< 20[9] Myr
32 Cyg B
Mass4.13[7] M
Radius3.0[7] R
Luminosity302[7] L
Temperature16,200[10] K
Other designations
ο2 Cyg, ο3 Cyg,[11] 32 Cyg, BD+47°3059, HIP 99848, HR 7751, SAO 49385, V1488 Cyg
A: HD 192909
B: HD 192910
Database references
32 Cyg A
32 Cyg B
32 Cygni

32 Cygni (32 Cyg, Omicron2 Cyg, ο2 Cyg) is the Flamsteed designation for a binary star system in the Cygnus constellation. It is a 4th magnitude star, which can be seen with the naked eye under suitably dark skies. Parallax measurements give an estimated distance of 1,100 light-years (320 parsecs) from the Earth.[1] However, Schröder et al. (2007) suggest the actual value, after correcting for Malmquist bias, may be closer to 1,174 light-years (360 parsecs).[7] Although it is a spectrsocopic binary with components that cannot be separated visually, it has two entries in the Henry Draper Catalogue, with identical magnitudes and positions, but showing the spectral types of the two components.[12]

The Bayer letter ο has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 32 Cygni has been designated as either ο2 or ο3 Cygni. For clarity, it is preferred to use the Flamsteed designation 32 Cygni rather than one of the Bayer designations.[11]

The primary component in this system, 32 Cygni A, has a stellar classification of K5 Iab, indicating that it is a supergiant star. Its effective temperature of 3,840 K lies in the range for K-type stars,[7] giving it an orange hue.[13] This star has more four than times the mass of the Sun and the outer envelope has expanded to about 184 times the Sun's radius.[7] It is radiating 6,600 times the luminosity of the Sun.[7]

The companion star, 32 Cygni B, is smaller than the primary, with four times the Sun's mass and three times the Sun's radius.[7] It has a much higher effective temperature of 16,200 K[10] and is radiating over 300 times the Sun's luminosity.[7] This star has the blue-white hue of a B7 star main sequence star.

The two stars form an eclipsing binary system (variable star designation: V1488 Cyg) similar to Algol. The orbital plane of the two stars is nearly aligned with the line of sight from the Earth, so that the giant star eclipses the secondary component once per orbit. During an eclipse, emission lines can be seen in the spectrum of this system. These originate in the stellar wind escaping from the giant star. In a volume around the B star, this wind becomes ionized, resulting in a circumstellar H II region.[14] The giant star is losing mass at the rate of 1.3 × 10−8 times the mass of the Sun per year, or the equivalent of the Sun's mass every 77 million years.[7]

The Washington Double Star Catalog and Catalog of Components of Double and Multiple Stars both list a visual companion 208" distant. This star is the 8th magnitude A class HD 192933.[15][16]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (November 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.
  2. 2.0 2.1 2.2 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode 1966CoLPL...4...99J.
  3. 3.0 3.1 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.
  4. Eggleton, P. P.; Tokovinin, A. A. (2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society 389 (2): 869. arXiv:0806.2878. Bibcode 2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  5. Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington (Carnegie Institution of Washington), Bibcode 1953GCRV..C......0W.
  6. Jancart, S. et al. (October 2005), "Astrometric orbits of SB^9 stars", Astronomy and Astrophysics 442 (1): 365–380, arXiv:astro-ph/0507695, Bibcode 2005A&A...442..365J, doi:10.1051/0004-6361:20053003.
  7. 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 Schröder, K.-P.; Cuntz, M. (April 2007), "A critical test of empirical mass loss formulas applied to individual giants and supergiants", Astronomy and Astrophysics 465 (2): 593–601, arXiv:astro-ph/0702172, Bibcode 2007A&A...465..593S, doi:10.1051/0004-6361:20066633.
  8. Cenarro, A. J. et al. (January 2007), "Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters", Monthly Notices of the Royal Astronomical Society 374 (2): 664–690, arXiv:astro-ph/0611618, Bibcode 2007MNRAS.374..664C, doi:10.1111/j.1365-2966.2006.11196.x.
  9. Kaler, James B., "OMI-2 CYG (Omicron-2 = 32 Cygni)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/omi2cyg.html, retrieved 2012-01-20.
  10. 10.0 10.1 Malkov, O. Yu. (December 2007), "Mass-luminosity relation of intermediate-mass stars", Monthly Notices of the Royal Astronomical Society 382 (3): 1073–1086, Bibcode 2007MNRAS.382.1073M, doi:10.1111/j.1365-2966.2007.12086.x.
  11. 11.0 11.1 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.
  12. Nesterov, V. V.; Kuzmin, A. V.; Ashimbaeva, N. T.; Volchkov, A. A.; Röser, S.; Bastian, U. (1995). "The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars". Astronomy and Astrophysics 110. Bibcode 1995A&AS..110..367N.
  13. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, archived from the original on March 10, 2012, https://www.webcitation.org/6630AbtJZ?url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16.
  14. Eaton, J. A. (November 2008), "Emission Lines in 32 Cygni", The Journal of Astronomical Data 14, Bibcode 2008JAD....14....3E.
  15. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. Bibcode 2001AJ....122.3466M. doi:10.1086/323920.
  16. Dommanget, J.; Nys, O. (1994). "Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition - Catalogue of the components of double and multiple stars (CCDM) first edition". Com. de l'Observ. Royal de Belgique 115: 1. Bibcode 1994CoORB.115....1D.

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