Epsilon Cygni

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Epsilon Cygni
Diagram showing star positions and boundaries of the Cygnus constellation and its surroundings
Cercle rouge 100%.svg

Location of ε Cygni (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
Distance 72.7 ± 0.2 ly
(22.29 ± 0.06 pc)
Absolute magnitude (MV) +0.78 ± 0.03[5]
Details
Mass ~2[6] M
Radius 10.82 ± 0.14[7] R
Luminosity 62 ± 3[7] L
Surface gravity (log g) 2.8[4] cgs
Temperature 4,710[4] K
Metallicity [Fe/H] –0.27[4] dex
Rotational velocity (v sin i) 3.0 ± 1.0[5] km/s
Age ~1.5[6] Gyr
Other designations
Gienah Cygni, 53 Cygni, BD +33°4018, FK5 780, GCTP 4959.00, Gl 806.1, HD 197989, HIP 102488, HR 7949, LHS 5358, SAO 70474.[8]
Database references
SIMBAD data

Epsilon Cygni (ε Cyg, ε Cygni) is a star in the constellation Cygnus. This Bayer designation is from Johann Bayer's 1603 Uranometria atlas of bright stars. With an apparent visual magnitude of 2.48,[2] which makes it readily visible to the naked eye at night and one of the brighter members of Cygnus. It is called Gienah, a traditional name it shares with Gamma Corvi. The name "Gienah" derives from the Arabic word for wing, جناح janāħ.[9] In Chinese, 天津 (Tiān Jīn), meaning Celestial Ford, refers to an asterism consisting of ε Cygni, γ Cygni, δ Cygni, 30 Cygni, α Cygni, ν Cygni, τ Cygni, υ Cygni and ζ Cygni.[10] Consequently, ε Cygni itself is known as 天津九 (Tiān Jīn jiǔ, English: the Ninth Star of Celestial Ford.).[11] Based upon parallax measurement, Epsilon Cygni is about 73 light-years from Earth.[1]

Epsilon Cygni is a giant star with a stellar classification of K0 III.[3] This indicates that the star has left the main sequence and has begun the final stages in its stellar evolution. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[12] The effective temperature of the star's photosphere is 4,710 K, giving Epsilon Cygni an orange hue that is a characteristic of K-type stars.[13] This star has nearly 11 times the solar radius and is about 62 times the luminosity of the Sun.[7]

In 1920 it was suggested that the star is a spectroscopic binary system, but this was later brought into question. It has an optical companion Epsilon Cygni B that is not physically associated with Epsilon Cygni A, and a 13th magnitude candidate common proper motion companion Epsilon Cygni C at an angular separation of 78 arcseconds.[14] 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] Radial velocity observations of Epsilon Cygni suggest a possible companion with an orbital period of at least 15 years.[14]

See also[edit]

References[edit]

  1. ^ a b c d e f 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  Note: see VizieR catalogue I/311.
  2. ^ a b c d 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. ^ a b 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 
  4. ^ a b c d 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. ^ a b Carney, Bruce W. et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892 
  6. ^ a b c Kaler, James, "GIENAH CYGNI (Epsilon Cygni)", Stars (University of Illinois), retrieved 2011-12-11 
  7. ^ a b c 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 
  8. ^ "LHS 5358b -- High proper-motion Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-10 
  9. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G.E. Stechert, p. 197 
  10. ^ (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.
  11. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  12. ^ 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 
  13. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  14. ^ a b 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 

External links[edit]