T Cygni

T Cygni is a binary star[9] 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]

T Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 47m 10.75239s[1]
Declination +34° 22′ 26.8374″[1]
Apparent magnitude (V) 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
Radial velocity (Rv)−23.9±0.3[6] km/s
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
A
Radius28.19+0.67
−0.86[1] R☉
Luminosity241.4±4.5[1] L☉
Surface gravity (log g)2.12[7] cgs
Temperature4,285+50
−67[1] K
Metallicity [Fe/H]−0.12[7] dex
Other designations
T Cyg, BD+33° 4028, HD 198134, HIP 102571, HR 7956, SAO 70499, WDS J20472+3422A[8]
Database references
SIMBADdata

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 star has expanded to 28 times the radius of the Sun.[1] It is radiating 241 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,285 K.[1]

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. Gaia DR2 record for this source at VizieR.
  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. S2CID 119257644.
  3. 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. 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. 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.
  6. 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. S2CID 119231169.
  7. 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.
  8. "T Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 September 2018.
  9. 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. S2CID 14878976.
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