# T Cygni

T Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 47m 10.75239s[1]
Declination +34° 22′ 26.8374″[1]
4.93[2] + 10.03[3]
Characteristics
Spectral type K3 III[4]
B−V color index 1.294±0.003[2]
Variable type Lb:[5]
Astrometry
Proper motion (μ) RA: +39.637[1] mas/yr
Dec.: +8.068[1] mas/yr
Parallax (π)8.4327 ± 0.1348[1] mas
Distance387 ± 6 ly
(119 ± 2 pc)
Absolute magnitude (MV)−0.74[2]
Details
T Cyg A
Luminosity333.48[2] L
Surface gravity (log g)2.12[8] cgs
Temperature4,190[8] K
Metallicity [Fe/H]−0.12[8] dex
Other designations
T Cyg, BD+33° 4028, HD 198134, HIP 102571, HR 7956, SAO 70499, WDS J20472+3422A[9]
Database references

T Cygni is a binary star[10] 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 8.4 mas,[1] it is located 387 light years away. It is moving closer to the Earth with a heliocentric radial velocity of −24 km/s.[6]

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.[5] It is a giant star with a stellar classification of K3 III,[4] which indicates it has exhausted the hydrogen at its core and evolved away from the main sequence. The measured angular diameter of this star, after correction for limb darkening, is 2.11±0.02 mas.[11] At the estimated distance of this star, this yields a physical size of about 27 times the Sun's radius.[7] It is radiating 333[2] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,190 K.[8]

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°).[3]

## References

1. 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.
2. 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.
3. ^ a b Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
4. ^ a b 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. Bibcode:1955ApJ...121..118H. doi:10.1086/145969.
5. ^ a b 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.
6. ^ a b Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
7. ^ a b Lang, Kenneth R. (2006). "Astrophysical formulae". Astronomy and astrophysics library. 1 (3 ed.). Birkhäuser. ISBN 3-540-29692-1.. The radius (R*) is given by:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(10^{-3}\cdot 118.6\cdot 2.11)\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 53.8\cdot R_{\bigodot }\end{aligned}}}
8. ^ a b c d McWilliam, Andrew (December 1990). "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances". Astrophysical Journal Supplement Series. 74: 1075–1128. Bibcode:1990ApJS...74.1075M. doi:10.1086/191527.
9. ^ "T Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 September 2018.
10. ^ 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.
11. ^ Richichi, A.; et al. (February 2005). "CHARM2: An updated Catalog of High Angular Resolution Measurements". Astronomy and Astrophysics. 431 (2): 773–777. Bibcode:2005A&A...431..773R. doi:10.1051/0004-6361:20042039.