R Cygni

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R Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 19h 36m 49.35633s[1]
Declination +50° 11′ 59.7198″[1]
Apparent magnitude (V) 6.1 - 14.4[2]
Spectral type S2.5,9e-S6,9e(Tc)[3]
B−V color index 0.101±0.019[4]
Variable type Mira[2]
Proper motion (μ) RA: −3.158[1] mas/yr
Dec.: −5.755[1] mas/yr
Parallax (π)1.4835 ± 0.0963[1] mas
Distance2,200 ± 100 ly
(670 ± 40 pc)
Radius745[a] R
Luminosity11,700[5] L
Temperature2,200[6] K
Other designations
R Cyg, BD+49 3064, HD 185456, HIP 31822, SAO 31822, WDS J19368+5012[7]
Database references
R Cygni light curve, showing the period-doubling

R Cygni is a variable star of the Mira type in the constellation Cygnus, less than 4' from θ Cygni. This is a red giant star on the asymptotic giant branch located around 2,200 light years away. It is an S-type star ranging between spectral types S2.5,9e to S6,9e(Tc).[3]

Stars at this mass range and evolutionary stage are pulsationally unstable, displaying a variation in their light output.[8] R Cygni has a maximum magnitude of 6.1 and a minimum magnitude of 14.4, with a period of 426.45 days.[2] The variation of this star was discovered by English astronomer N. R. Pogson in 1852, and it has a history of recorded brightness measurements stretching back more than a century.[8] R Cygni shows distinct period-doubling, where alternate maxima are of different brightness, hence the real period of pulsation could be considered to be twice that from one maximum to the next.[9]

The Catalog of Components of Double and Multiple Stars lists 10th magnitude BD+49 3065 as a companion to R Cygni, at a separation of 91", and both stars lie at approximately the same distance. The Washington Double Star Catalog additionally lists a 15th magnitude star as a companion at a separation of about 14".[10]


  1. ^ Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:


  1. ^ a b c d e 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.
  2. ^ a b c Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ a b BSJ (4 January 2010). "R Cygni". AAVSO Website. American Association of Variable Star Observers. Retrieved 21 January 2014.
  4. ^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  5. ^ Guandalini, R; Francis, Charles (2010). "Infrared photometry and evolution of mass-losing AGB stars. III. Mass loss rates of MS and S stars". Astronomy and Astrophysics. 513: A4. arXiv:1002.2458. Bibcode:2010A&A...513A...4G. doi:10.1051/0004-6361/200911764. S2CID 119193286.
  6. ^ Ramstedt, S; Schöier, F. L; Olofsson, H (2009). "Circumstellar molecular line emission from S-type AGB stars: Mass-loss rates and SiO abundances". Astronomy and Astrophysics. 499 (2): 515. arXiv:0903.1672. Bibcode:2009A&A...499..515R. doi:10.1051/0004-6361/200911730. S2CID 17942939.
  7. ^ "R Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 30 August 2018.
  8. ^ a b Kiss, L. L.; Szatmáry, K. (August 2002). "Period-doubling events in the light curve of R Cygni: Evidence for chaotic behaviour". Astronomy and Astrophysics. 390 (2): 585–596. arXiv:astro-ph/0205334. Bibcode:2002A&A...390..585K. doi:10.1051/0004-6361:20020744. S2CID 17698877.
  9. ^ Kiss, L. L; Szatmáry, K (2002). "Period-doubling events in the light curve of R Cygni: Evidence for chaotic behaviour". Astronomy & Astrophysics. 390 (2): 585–596. arXiv:astro-ph/0205334. Bibcode:2002A&A...390..585K. doi:10.1051/0004-6361:20020744. S2CID 17698877.
  10. ^ 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.