Epsilon Cygni

Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is multiple star system in the constellation of Cygnus. With an apparent visual magnitude of 2.48, it is readily visible to the naked eye at night as one of the brighter members of Cygnus. Based upon parallax measurement, Epsilon Cygni is about 73 light-years from the Sun.

Epsilon Cygni
Location of ε Cyg (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 46m 12.68236s[1]
Declination +33° 58′ 12.9250″[1]
Apparent magnitude (V) 2.480[2]
Characteristics
Spectral type K0 III[3]
U−B color index +0.860[2]
B−V color index +1.030[2]
Astrometry
Radial velocity (Rv)–12.41[4] km/s
Proper motion (μ) RA: 355.66[1] mas/yr
Dec.: 330.60[1] mas/yr
Parallax (π)44.86 ± 0.12[1] mas
Distance72.7 ± 0.2 ly
(22.29 ± 0.06 pc)
Absolute magnitude (MV)+0.74 ± 0.02[3]
Orbit[3]
Primaryε Cyg Aa
Companionε Cyg Ab
Period (P)55.1 yr
Eccentricity (e)0.9
Periastron epoch (T)B2016.00
Argument of periastron (ω)
(primary)		300°
Semi-amplitude (K1)
(primary)		4.0 km/s
Details
Mass~2[3] M☉
Radius10.82 ± 0.14[5] R☉
Luminosity62 ± 3[5] L☉
Surface gravity (log g)2.8[4] cgs
Temperature4,710[4] K
Metallicity [Fe/H]–0.27[4] dex
Rotation0.67 years[3]
Rotational velocity (v sin i)2.3 ± 0.2[3] km/s
Age~1.5[6] Gyr
Other designations
Aljanah, Gienah,[7] ε Cyg, 53 Cygni, BD +33°4018, FK5 780, GCTP 4959.00, Gl 806.1, HD 197989, HIP 102488, HR 7949, LHS 5358, SAO 70474, WDS 20462+3358.[8]
Database references
SIMBADdata

The system has three constituents: a spectroscopic binary (designated Epsilon Cygni A); an optical companion (B) and a single star (C). A's two components are themselves designated Epsilon Cygni Aa (officially named Aljanah /ˈældʒənə/) and Ab.

Nomenclature

ε Cygni (Latinised to Epsilon Cygni) is the system's Bayer designation. The designations of the three constituents as Epsilon Cygni A, B and C, and those of A's components - Epsilon Cygni Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[9]

Epsilon Cygni bore the traditional name Gienah from the Arabic al janāħ (Arabic: جناح‎) meaning "the wing".[10] However that name was more usually applied to Gamma Corvi.[7] For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized a Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[12] It approved the name Aljanah for the component Epsilon Cygni Aa on 30 June 2017. It had previously approved the name Gienah for Gamma Corvi A on 6 November 2016. Both are now so included in the List of IAU-approved Star Names.[13]

In Chinese astronomy, the "Celestial Ford" (Chinese: 天津; pinyin: Tiān Jīn) refers to an asterism consisting of Epsilon Cygni, Gamma Cygni, Delta Cygni, 30 Cygni, Alpha Cygni, Nu Cygni, Tau Cygni, Upsilon Cygni and Zeta Cygni.[14] Consequently, the Chinese name for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" (Chinese: 天津九; pinyin: Tiān Jīn jiǔ).[15]

Companions

Epsilon Cygni A has an optical companion, Epsilon Cygni B, with which it is not physically associated, and a 13th magnitude candidate common proper motion companion, Epsilon Cygni C, at an angular separation of 78 arcseconds.[16] If the latter star is gravitationally bound to Epsilon Cygni A, then they are currently separated by 1700 AU or more, and have an orbital period of at least 50,000 years.[6]

Properties
ε Cygni appears north of the Veil nebula towards the bottom left

Epsilon Cygni A is a single-lined spectroscopic binary.[17] Radial velocity observations suggest a possible companion with an orbital period of at least 15 years.[16] It presents as a giant star with a stellar classification of K0 III.[18] This indicates that the star has left the main sequence and has begun the final stages in its stellar evolution. The effective temperature of its photosphere is 4,710 K, giving an orange hue that is a characteristic of K-type stars.[19] It has nearly 11 times the solar radius and is about 62 times the luminosity of the Sun.[5]

Since 1943, the spectrum of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.[20]

Veil Nebula
Main article: Veil nebula

ε Cygni lies about three degrees north of the Veil nebula, a probable ancient supernova remnant. The nebula is far more distant than the star.

References
  1. van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752v1, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600 Note: see VizieR catalogue I/311.
  2. Oja, T. (August 1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–409, Bibcode:1986A&AS...65..405O
  3. Gray, David F. (2015). "A Spectroscopic Analysis of the K0 III Binary ε Cygni". The Astrophysical Journal. 810 (2): 117. Bibcode:2015ApJ...810..117G. doi:10.1088/0004-637X/810/2/117.
  4. 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, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  5. Piau, L.; et al. (February 2011), "Surface convection and red-giant radius measurements", Astronomy and Astrophysics, 526: A100, arXiv:1010.3649, Bibcode:2011A&A...526A.100P, doi:10.1051/0004-6361/201014442, S2CID 118533297
  6. Kaler, James, "GIENAH CYGNI (Epsilon Cygni)", Stars, University of Illinois, retrieved 2011-12-11
  7. Rumrill, H. B. (1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. 48 (283): 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681.
  8. "LHS 5358b -- High proper-motion Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-10
  9. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  10. Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G.E. Stechert: 197, Bibcode:1899sntm.book.....A
  11. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  12. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  13. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  14. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  15. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  16. McMillan, R. S.; Smith, P. H.; Moore, T. L.; Perry, M. L. (December 1992), "Variation of the radial velocity of Epsilon Cygni A", Publications of the Astronomical Society of the Pacific, 104 (682): 1173–1176, Bibcode:1992PASP..104.1173M, doi:10.1086/133105
  17. "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 14 February 2011. Retrieved 2 January 2018.
  18. Cohen, Martin; et al. (April 1999), "Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra", The Astronomical Journal, 117 (4): 1864–1889, Bibcode:1999AJ....117.1864C, doi:10.1086/300813
  19. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16
  20. Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04
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