RW Cygni

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RW Cygni
Sadr Region rgb.jpg
Region around γ Cygni, with RW Cygni annotated on the full-size image (north is right)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 28m 50.59095s[1]
Declination 39° 58′ 54.4268″[1]
Apparent magnitude (V) 8.05 - 9.70[2]
Spectral type M2-4Ia-Iab[2]
Variable type SRc[2]
Parallax (π)0.91 ± 1.03[1] mas
Distance~3,600[3] ly
Absolute magnitude (MV)-6.41[4]
Radius680[5] - 980[4] R
Diameter680[5] - 980[4] D
Luminosity145,000[6]–156,000[5] L
Temperature3,600[6]-3,920[5] K
Database references

RW Cygni is a semiregular variable star in the constellation Cygnus, about a degree east of 2nd magnitude γ Cygni. Its apparent magnitude varies between 8.05 and 9.70 and its spectral type between M2 and M4.


The Hipparcos parallax for RW Cygni is 0.91 mas but with a very large margin of error.[1] RW Cygni is assumed to be a member of the Cygnus OB9 Stellar Association and therefore around 3,600 light-years from the solar system.[4]


RW Cygni is a red supergiant with a bolometric luminosity around 150,000 L.[6][5][4] Its spectral type is given in the General Catalogue of Variable Stars as M2-4Ia-Iab, and one of the most recent catalogues of MK spectral classifications gives M3-M4Ia-Iab.[7] The effective temperature is directly calculated to be 3,600 K, giving a radius of 980 D.[4] An alternate calculation gives a higher temperature of 3,920 K and a correspondingly lower radius of 680 D.[5] Using the more conservative figure, if it was placed at the center of Solar System, it would be extend past the orbit of Mars and into the Asteroid Belt.

The initial mass of RW Cygni has been estimated from its position relative to theoretical stellar evolutionary tracks to be around 20 M. Observations of its atmosphere suggest that it is losing mass at a rate of 3.2×10−9 M per year.[5]

RW Cygni is classified as a semiregular variable star. It is given the subtype SRc, indicating that it is a cool supergiant.[2] Its brightness varies from extremes of magnitude +8.0 and +9.5 with a period of 580 ± 80 days. No long secondary period has been detected.[8]

See also[edit]


  1. 1.0 1.1 1.2 1.3 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 2.2 2.3 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. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics 405: 165. arXiv:astro-ph/0409579. Bibcode 2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  4. 4.0 4.1 4.2 4.3 4.4 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.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 Josselin, E.; Plez, B. (2007). "Atmospheric dynamics and the mass loss process in red supergiant stars". Astronomy and Astrophysics 469 (2): 671. arXiv:0705.0266. Bibcode 2007A&A...469..671J. doi:10.1051/0004-6361:20066353.
  6. 6.0 6.1 6.2 Mauron, N.; Josselin, E. (2011). "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.
  7. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series 71: 245. Bibcode 1989ApJS...71..245K. doi:10.1086/191373.
  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. arXiv:astro-ph/0608438. Bibcode 2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x.

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