RW Cygni

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 50.59027s[1]
Declination 39° 58′ 54.4180″[1]
Apparent magnitude (V) 8.05 - 9.70[2]
Characteristics
Evolutionary stage Red supergiant
Spectral type M3-4Ia-Iab[3]
Variable type SRc[2]
Astrometry
Radial velocity (Rv)−18.39±0.52[1] km/s
Proper motion (μ) RA: –3.255[1] mas/yr
Dec.: –5.511[1] mas/yr
Parallax (π)0.4602 ± 0.0897 mas[1]
Distance1,620+40
−40[4] pc
Absolute magnitude (MV)–6.41[5]
Details
Radius1,000[6] R☉
Luminosity126,000[4] - 160,000[6] L☉
Temperature3,605±170[6] K
Other designations
RW Cyg, BD+39 4208, HIP 101023, IRAS 20270+3948, 2MASS J20285059+3958543
Database references
SIMBADdata

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 M3 and M4.

Distance

The Gaia Data Release 2 parallax for RW Cyg is 0.4602±0.0897 mas or a distance of around 2.2 kpc.[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.[5][7] Newer observations based on the parallaxes of neighbouring OB stars give RW Cygni a distance of 1.62 kpc.[4]

Properties

RW Cygni is a luminous red supergiant with a bolometric luminosity more than 100,000 L☉.[8][5] Its spectral type is given in the General Catalogue of Variable Stars as M2-4Ia-Iab, covering the range of previously published values. It has been defined as a standard star for the MK spectral classification of M3-M4Ia-Iab.[3] In 2005, the effective temperature is directly calculated to be 3,600 K, giving a radius of 980 R☉.[5] An alternate calculation gives a higher temperature of 3,920 K and a correspondingly lower radius of 680 R☉.[8] More recent measurements based on its Gaia Data Release 2 parallax gives the similar effective temperature derived in 2005 and as well as a larger radius of 1,000 R☉, which would make RW Cygni one of the largest known stars.[6] 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.

A light curve for RW Cygni, plotted from Hipparcos data[9]

The initial mass of RW Cygni has been estimated from its position relative to theoretical stellar evolutionary tracks to be around 20 M☉.[8] Observations of its atmosphere suggest that it is losing mass at a rate of 3.2×10−6 M☉ per year.[10]

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 d. No long secondary period has been detected.[11]

See also

References

  1. 1 2 3 4 5 6 7 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. 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (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. 1 2 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. S2CID 123149047.
  4. 1 2 3 Davies, Ben; Beasor, Emma R. (March 2020). "The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors". MNRAS. 493 (1): 468–476. arXiv:2001.06020. Bibcode:2020MNRAS.493..468D. doi:10.1093/mnras/staa174. S2CID 210714093.
  5. 1 2 3 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): 973–985. arXiv:astro-ph/0504337. Bibcode:2005ApJ...628..973L. doi:10.1086/430901. S2CID 15109583.
  6. 1 2 3 4 Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  7. ↑ 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. S2CID 17804304.
  8. 1 2 3 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. S2CID 17789027.
  9. ↑ "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
  10. ↑ 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. S2CID 119276502.
  11. ↑ 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): 1721–1734. arXiv:astro-ph/0608438. Bibcode:2006MNRAS.372.1721K. doi:10.1111/j.1365-2966.2006.10973.x. S2CID 5203133.
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