Astronomy:Zeta Cygni

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Short description: Star in the constellation Cygnus
Zeta Cygni
Location of ζ Cygni (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cygnus
Right ascension  21h 12m 56.186s[1]
Declination +30° 13′ 36.835″[1]
Apparent magnitude (V) 3.26[2]
Characteristics
Evolutionary stage Giant + white dwarf
Spectral type G8IIIa + DA4.2[3]
U−B color index +0.77[2]
B−V color index +0.98[2]
Astrometry
Radial velocity (Rv)+15.85 ± 0.26[4] km/s
Proper motion (μ) RA: −3.792[1] mas/yr
Dec.: −45.429[1] mas/yr
Parallax (π)21.8130 ± 0.1375[1] mas
Distance149.5 ± 0.9 ly
(45.8 ± 0.3 pc)
Absolute magnitude (MV)–0.01[5]
Orbit[6]
Period (P)6,489 ± 31 days
Semi-major axis (a)0.19″[7]
Eccentricity (e)0.22 ± 0.03
Periastron epoch (T)40,712 ± 178 MJD
Argument of periastron (ω)
(secondary)		41 ± 10°
Semi-amplitude (K1)
(primary)		3.31 ± 0.12 km/s
Details
ζ Cyg A
Mass3.05[8] M☉
Radius15[4] R☉
Luminosity112[4] L☉
Surface gravity (log g)2.41[5] cgs
Temperature4,910[5] K
Metallicity [Fe/H]–0.04[5] dex
Rotational velocity (v sin i)0.4 ± 0.5[8] km/s
Age0.2[9] Gyr
ζ Cyg B
Mass0.6[7] M☉
Temperature12,000[7] K
Other designations
Tianjinnan, ζ Cyg, 64 Cyg, BD+29°4348, HD 202109, HIP 104732, HR 8115, SAO 71070[10]
Database references
SIMBADdata

Zeta Cygni is a binary star system in the northern constellation of Cygnus, the swan. It has the proper name Tianjinnan;[11] Zeta Cygni is its Bayer designation, which is Latinized from ζ Cygni and abbreviated Zeta Cyg or ζ Cyg. The system has a combined apparent visual magnitude of 3.26 and, based upon parallax measurements, is about 143 light-years (44 parsecs) away.

Observations

The primary component, ζ Cyg A is a giant star with a spectral type of G8 IIIp. Its most likely status is as a red clump giant,[citation needed] an evolved star that has begun core helium fusion. It has around three times the mass of the Sun and has expanded to about 15 times the Sun's radius. It is radiating 112 times the brightness of the Sun from its outer atmosphere at an effective temperature of 4,910 K. At this temperature, the star glows with the yellow hue of a G-type star.[12]

The secondary component, ζ Cyg B, is a white dwarf of type DA4.2. The pair orbit each other every 6,489 days (17.8 years) with an eccentricity of 0.22. The white dwarf cannot be seen directly, but is estimated to have an apparent magnitude of 13.2.[3]

Zeta Cygni A has an overabundance of barium, as well as other heavy chemical elements in its atmosphere, making it a so-called "mild" barium star. These elements were synthesized by the other member of the system as it passed through the asymptotic giant branch (AGB) stage of its evolution, then ejected in its stellar wind and accreted onto the current primary component. Prior to acquiring this additional mass, Zeta Cygni A had about 2.5 times the mass of the Sun, while the more evolved AGB star had three solar masses.[8]

In Chinese astronomy, this is the southernmost star of the constellation Tianjin, the Celestial Ferry. This constellation figures in the story of the Cowherd and the Weaver Girl (Altair and Vega), allowing the lovers to cross the Milky Way and meet once a year. The IAU Working Group on Star Names adopted the name Tianjinnan ("nan" meaning south) for Zeta Cygni A on 16 July 2026.[11]

References

  1. ↑ 1.0 1.1 1.2 1.3 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.
  2. ↑ 2.0 2.1 2.2 Fernie, J. D. (May 1983), "New UBVRI photometry for 900 supergiants", Astrophysical Journal Supplement Series 52: 7–22, doi:10.1086/190856, Bibcode: 1983ApJS...52....7F. 
  3. ↑ 3.0 3.1 Holberg, J. B. et al. (2013), "Where are all the Sirius-like binary systems?", Monthly Notices of the Royal Astronomical Society 435 (3): 2077, doi:10.1093/mnras/stt1433, Bibcode: 2013MNRAS.435.2077H. 
  4. ↑ 4.0 4.1 4.2 Massarotti, Alessandro et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal 135 (1): 209–231, doi:10.1088/0004-6256/135/1/209, Bibcode: 2008AJ....135..209M. 
  5. ↑ 5.0 5.1 5.2 5.3 Allen, D. M.; Porto de Mello, G. F. (January 2011), "Mn, Cu, and Zn abundances in barium stars and their correlations with neutron capture elements", Astronomy and Astrophysics 525: A63, doi:10.1051/0004-6361/200912356, Bibcode: 2011A&A...525A..63A. 
  6. ↑ Griffin, R. F.; Keenan, P. C. (August 1992), "Spectroscopic binary orbits from photoelectric radial velocities. Paper 105: zeta Cygni", The Observatory 112: 168–182, Bibcode: 1992Obs...112..168G. 
  7. ↑ 7.0 7.1 7.2 Barstow, M. A. et al. (April 2001), "Resolving Sirius-like binaries with the Hubble Space Telescope", Monthly Notices of the Royal Astronomical Society 322 (4): 891–900, doi:10.1046/j.1365-8711.2001.04203.x, Bibcode: 2001MNRAS.322..891B. 
  8. ↑ 8.0 8.1 8.2 Yushchenko, A. V. et al. (January 2004), "The chemical composition of the mild barium star HD 202109", Astronomy and Astrophysics 413 (3): 1105–1114, doi:10.1051/0004-6361:20031596, Bibcode: 2004A&A...413.1105Y. 
  9. ↑ Smiljanic, R. et al. (June 2007), "Abundance analysis of barium and mild barium stars", Astronomy and Astrophysics 468 (2): 679–693, doi:10.1051/0004-6361:20065867, Bibcode: 2007A&A...468..679S. 
  10. ↑ "zet Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=zet+Cyg. 
  11. ↑ 11.0 11.1 IAU Catalog of Star Names, International Astronomical Union, https://exopla.net/star-names/modern-iau-star-names/, retrieved 19 July 2026. 
  12. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16 

Coordinates: Sky map 21h 12m 56.18594s, +30° 13′ 36.8957″



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