Astronomy:T Cygni

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Short description: Variable star in the constellation Cygnus
Not to be confused with Tau Cygni.
T Cygni
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A visual band light curve for T Cygni, plotted from AAVSO data[1]
Observation data
{{#ifeq:J2000|J2000.0 (ICRS)|Epoch J2000.0      Equinox J2000.0 (ICRS)| Epoch J2000      [[Astronomy:Equinox (celestial coordinates)|Equinox J2000}}
Constellation Cygnus[2]
A
Right ascension  20h 47m 10.75235s[3]
Declination +34° 22′ 26.8411″[3]
Apparent magnitude (V) 4.91 - 4.96[4]
B
Right ascension  20h 47m 11.44798s[5]
Declination +34° 22′ 21.7891″[5]
Apparent magnitude (V) 10.03[6]
Characteristics
Evolutionary stage Red-giant branch[3] (A)
Spectral type K3 III[7]
B−V color index 1.294±0.003[2]
Variable type Lb:[4]
Astrometry
A
Radial velocity (Rv)−23.9±0.3[8] km/s
Proper motion (μ) RA: +39.640[3] mas/yr
Dec.: +7.826[3] mas/yr
Parallax (π)7.7834 ± 0.0730[5] mas
Distance419 ± 4 ly
(128 ± 1 pc)
Absolute magnitude (MV)−0.74[2]
B
Proper motion (μ) RA: +39.613[5] mas/yr
Dec.: +7,558[5] mas/yr
Parallax (π)7.8768 ± 0.0173[5] mas
Distance414.1 ± 0.9 ly
(127.0 ± 0.3 pc)
Details
A
Mass4.5[3] M☉
Radius35[3] R☉
Luminosity374[3] L☉
Surface gravity (log g)2.00[9] cgs
Temperature4,423[10] K
Metallicity [Fe/H]−0.08[9] dex
Rotational velocity (v sin i)1.0[11] km/s
B
Mass0.81[10] M☉
Radius0.86[5] R☉
Luminosity0.37[5] L☉
Surface gravity (log g)4.49[5] cgs
Temperature4.866[5] K
Other designations
T Cyg, BD+33°4028, HD 198134, HIP 102571, HR 7956, SAO 70499, WDS J20472+3422AB[12][13]
Database references
SIMBADdata

T Cygni is a binary star[14] system in the northern constellation of Cygnus. It is a faint system but visible to the naked eye with a combined apparent visual magnitude of 4.93.[2] Based upon an annual Parallax shift of 7.8 mas, it is located about 414 light years away. It is moving closer to the Earth with a heliocentric radial velocity of −24 km/s.

The primary, component A, is a variable star, most likely of the slow irregular type, which ranges in magnitude from 4.91 down to 4.96.[4] Johann Friedrich Julius Schmidt discovered that its brightness varies, in 1864. It appeared with its variable star designation in Annie Jump Cannon's 1907 work "Second Catalogue of Variable Stars".[15] It is a giant star with a stellar classification of K3 III,[7] which indicates it has exhausted the hydrogen at its core and evolved away from the main sequence. The star has expanded to 35 times the radius of the Sun. It is radiating 374 times the Sun's luminosity from its enlarged photosphere[3] at an effective temperature of 4,423 K.[10]

The secondary companion, component B, is a magnitude 10.03 star located at an angular separation of 8.10″ along a position angle of 120°, as of 2012. In 1877 it was separated by 10.0″ with nearly the same position angle (121°).[6] Although no spectral class has been published, the secondary has been calculated to have a mass of 0.8 M☉,[10] an effective temperature of 4,866 K, a radius of 0.9 R☉, and a bolometric luminosity of 0.4 L☉.[5]

Multiple star catalogs list an 11th magnitude star, component C, at a separation of 17″.[16] It has a small parallax and is much further away than the binary pair.[17]

References

  1. ↑ "Download Data". AAVSO. https://www.aavso.org/data-download. 
  2. ↑ 2.0 2.1 2.2 2.3 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  4. ↑ 4.0 4.1 4.2 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. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  6. ↑ 6.0 6.1 Mason, B. D. et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal 122 (6): 3466–3471. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 
  7. ↑ 7.0 7.1 Herbig, George H.; Spalding, John F. Jr. (January 1955). "Axial Rotation and Line Broadening in Stars of Spectral Types F0-K5". Astrophysical Journal 121: 118. doi:10.1086/145969. Bibcode: 1955ApJ...121..118H. 
  8. ↑ Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759–771. doi:10.1134/S1063773706110065. Bibcode: 2006AstL...32..759G. 
  9. ↑ 9.0 9.1 Khalatyan, A.; Anders, F.; Chiappini, C.; Queiroz, A. B. A.; Nepal, S.; Dal Ponte, M.; Jordi, C.; Guiglion, G. et al. (2024). "Transferring spectroscopic stellar labels to 217 million Gaia DR3 XP stars with SHBoost". Astronomy and Astrophysics 691: A98. doi:10.1051/0004-6361/202451427. Bibcode: 2024A&A...691A..98K. 
  10. ↑ 10.0 10.1 10.2 10.3 Stassun, Keivan G. et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S. 
  11. ↑ De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series 139 (3): 433. doi:10.1051/aas:1999401. Bibcode: 1999A&AS..139..433D. 
  12. ↑ "T Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=T+Cyg. 
  13. ↑ "T Cyg B". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=T+Cyg+B. 
  14. ↑ 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. doi:10.1111/j.1365-2966.2008.13596.x. Bibcode: 2008MNRAS.389..869E. 
  15. ↑ Cannon, Annie J. (1907). "Second Catalogue of Variable Stars". Annals of Harvard College Observatory 55: 1-94. https://articles.adsabs.harvard.edu/pdf/1907AnHar..55....1C. Retrieved 26 March 2025. 
  16. ↑ 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. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 
  17. ↑ Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.



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