T Cygni
{{short description|Variable star in the constellation Cygnus}}
{{distinguish|Tau Cygni}}
{{Starbox begin}}
{{Starbox image
| image = 250px
| caption = A visual band light curve for T Cygni, plotted from AAVSO data
}}
{{Starbox observe 2s
| epoch = J2000
| constell = Cygnus
| component1 = A
| dec1 = {{DEC|+34|22|26.8411}}
| component2 = B
| dec2 = {{DEC|+34|22|21.7891}}
}}
{{Starbox character
| type = Red-giant branch (A)
| u-b =
| variable = Lb:
}}
{{Starbox astrometry
| component1 = A
| radial_v = {{Val|−23.9|0.3}}
| parallax = 7.7834
| p_error = 0.0730
| component2 = B
| radial_v2 =
| parallax2 = 7.8768
| p_error2 = 0.0173
| absmag_v2 =
}}
{{Starbox detail
| source =
| component1 = A
| age_myr =
| component2 = B
| rotational_velocity2 =
| age_myr2 =
}}
{{Starbox catalog
| names={{odlist | V=T Cyg | BD=+33°4028 | HD=198134 | HIP=102571 | HR=7956 | SAO=70499 | WDS=J20472+3422AB | AAVSO=2043+34 }}
}}
{{Starbox reference
| Simbad = T+Cyg
}}
{{Starbox end}}
T Cygni is a binary star 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. Based upon an annual Parallax shift of {{Val|7.8|ul=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. 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". It is a giant star with a stellar classification of K3 III, 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 at an effective temperature of {{val|fmt=commas|4423|ul=K}}.
The secondary companion, component B, is a magnitude 10.03 star located at an angular separation of {{Val|8.10|ul=arcsecond}} along a position angle of 120°, as of 2012. In 1877 it was separated by {{Val|10.0|ul=arcsecond}} with nearly the same position angle (121°). Although no spectral class has been published, the secondary has been calculated to have a mass of {{solar mass|0.8|link=y}}, an effective temperature of {{val|fmt=commas|4866|u=K}}, a radius of {{solar radius|0.9}}, and a bolometric luminosity of {{solar luminosity|0.4|link=y}}.
Multiple star catalogs list an 11th magnitude star, component C, at a separation of {{val|17|u="}}. It has a small parallax and is much further away than the binary pair.
References
{{reflist|refs=
{{cite simbad | title=T Cyg | access-date=27 March 2025 }}
{{cite simbad | title=T Cyg B | access-date=27 March 2025 }}
{{cite Gaia DR3|1869341845103357312}}
{{cite Gaia DR3|1869341845103356928}}
{{cite Gaia DR3|1869341845090915968}}
| title=XHIP: An extended hipparcos compilation
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| journal=Astronomy Letters | arxiv=1108.4971
| volume=38 | issue=5 | pages=331 | year=2012
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | s2cid=119257644 }}
| title=General catalogue of variable stars: Version GCVS 5.1
| last1=Samus' | first1=N. N | last2=Kazarovets | first2=E. V
| last3=Durlevich | first3=O. V | last4=Kireeva | first4=N. N
| last5=Pastukhova | first5=E. N | journal=Astronomy Reports
| volume=61 | issue=1 | pages=80 | year=2017
| doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=125853869 }}
| title=A catalogue of multiplicity among bright stellar systems
| last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A.
| journal=Monthly Notices of the Royal Astronomical Society
| volume=389 | issue=2 | pages=869 | date=2008
| doi=10.1111/j.1365-2966.2008.13596.x
| doi-access=free | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }}
| last1=Herbig | first1=George H.
| last2=Spalding | first2=John F. Jr.
| title=Axial Rotation and Line Broadening in Stars of Spectral Types F0-K5
| journal=Astrophysical Journal
| volume=121 | page=118 | date=January 1955
| doi=10.1086/145969 | bibcode=1955ApJ...121..118H }}
| last1=Gontcharov | first1=G. A.
| title=Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system
| journal=Astronomy Letters
| volume=32| issue=11| pages=759–771| date=November 2006
| doi = 10.1134/S1063773706110065| bibcode=2006AstL...32..759G
|arxiv = 1606.08053 | s2cid=119231169
}}
| display-authors=1 | last1=Mason | first1=B. D.
| last2=Wycoff | first2=G. L. | last3=Hartkopf | first3=W. I.
| last4=Douglass | first4=G. G. | last5=Worley | first5=C. E.
| title=The Washington Visual Double Star Catalog
| journal=The Astronomical Journal
| volume=122 | issue=6 | pages=3466–3471 | date=2014
| bibcode=2001AJ....122.3466M | doi=10.1086/323920 | doi-access=free }}
| last1=Cannon | first1=Annie J. | title=Second Catalogue of Variable Stars | journal=Annals of Harvard College Observatory
| date=1907 | volume=55 | pages=1-94 | url=https://articles.adsabs.harvard.edu/pdf/1907AnHar..55....1C
| access-date=26 March 2025}}
}}
{{Stars of Cygnus}}
Category:Slow irregular variables
Category:Cygnus (constellation)