Astronomy:Epsilon Cygni

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Short description: Star in the constellation Cygnus
Epsilon Cygni
Location of ε Cyg (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cygnus
Right ascension  20h 46m 12.68236s[1]
Declination +33° 58′ 12.9250″[1]
Apparent magnitude (V) 2.480[2]
Characteristics
Evolutionary stage Horizontal branch[3]
Spectral type K0 III[4]
U−B color index +0.860[2]
B−V color index +1.030[2]
Astrometry
Radial velocity (Rv)−12.41[5] 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[4]
Orbit[3]
Primaryε Cyg Aa
Companionε Cyg Ab
Period (P)53.693+0.321
−0.328 yr
Semi-major axis (a)15.8±0.2 astronomical unit|AU
Eccentricity (e)0.9295±0.0003
Argument of periapsis (ω)
(primary)		275.30±0.06°
Semi-amplitude (K1)
(primary)		4.6 km/s
Details
A
Mass1.103±0.042[3] M☉
Radius11.13[6] R☉
Luminosity56.4±0.6[7] L☉
Surface gravity (log g)2.79±0.23[7] cgs
Temperature4,699[6] K
Metallicity [Fe/H]−0.126[6] dex
Rotation0.67[4] years
Rotational velocity (v sin i)2.3 ± 0.2[4] km/s
Age9.62±0.12[3] Gyr
B
Mass≥0.265±0.007[3] M☉
Other designations
Aljanah, Gienah,[8] 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[9]
Database references
SIMBADdata

Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is a binary star in the constellation of Cygnus. With an apparent visual magnitude of 2.48, it is readily visible to the naked eye at night, and is the third-brightest star in the constellation. Based upon parallax measurement, Epsilon Cygni is about 73 light-years distant.

The system has two confirmed constituents, Epsilon Cygni Aa (officially named Aljanah /ˈældʒənə/) and Ab. Additionally, a visual companion (Epsilon Cygni C) is likely bound to the system.[3]

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).[10]

Epsilon Cygni bore the traditional name Gienah from the Arabic al janāħ (Arabic: جناح) meaning "the wing".[11] However that name was more usually applied to Gamma Corvi.[8] For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[13] 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.[14]

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.[15] Consequently, the Chinese name for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" (Chinese: 天津九; pinyin: Tiān Jīn jiǔ).[16]

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.[17] If the latter star is gravitationally bound to Epsilon Cygni A, then they are currently separated by 1,700 AU or more, and have an orbital period of at least 50,000 years.[18]

Properties

ε Cygni appears north of the Veil Nebula towards the bottom left

Epsilon Cygni A is a single-lined spectroscopic binary.[19] The components take 53 years to complete an orbit and are in a highly eccentric orbit, which put their distances from 1.1 astronomical units in apoapsis to 30.5 astronomical units in periapsis.[3][lower-alpha 1] Its main component is a giant star with a stellar classification of K0 III.[20] This indicates that the star has left the main sequence and has begun the final stages in its stellar evolution. After passing through the red-giant branch stage, it underwent a helium flash event and is now a horizontal branch star generating energy through the thermonuclear fusion of helium at its core.[3] The effective temperature of its photosphere is 4,700 K,[6] giving an orange hue that is a characteristic of K-type stars.[21] Being 10% more massive than the Sun and nine billion years old,[3] it has 11 times the radius of the Sun[6] and is about 56 times more luminous.[7]

The secondary has never been observed directly, its existence was inferred solely on astronomical spectroscopy. Based on this data, it should have a mass of at least 0.265 M☉.[3]

Since 1943, the spectrum of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.[22]

Veil Nebula

Main article: Astronomy: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.

Notes

  1. ↑ Calculated using semi-major axis of 15.8 AU and eccentricity of 0.93 via the equations SMA(1−e) for apoastron and SMA(1+e) for periastron.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V  Note: see VizieR catalogue I/311.
  2. ↑ 2.0 2.1 2.2 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. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 Heeren, Paul; Reffert, Sabine; Trifonov, Trifon; Wong, Ka Ho; Lee, Man Hoi; Lillo-Box, Jorge; Quirrenbach, Andreas; Arentoft, Torben et al. (2021-03-01), "Precise radial velocities of giant stars - XV. Mysterious nearly periodic radial velocity variations in the eccentric binary ε Cygni" (in en), Astronomy & Astrophysics 647: A160, doi:10.1051/0004-6361/202040087, ISSN 0004-6361, Bibcode: 2021A&A...647A.160H 
  4. ↑ 4.0 4.1 4.2 4.3 Gray, David F. (2015). "A Spectroscopic Analysis of the K0 III Binary ε Cygni". The Astrophysical Journal 810 (2): 117. doi:10.1088/0004-637X/810/2/117. Bibcode: 2015ApJ...810..117G. 
  5. ↑ 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 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Gray, David F.; Kaur, Taranpreet (2019-09-01), "A Recipe for Finding Stellar Radii, Temperatures, Surface Gravities, Metallicities, and Masses Using Spectral Lines", The Astrophysical Journal 882 (2): 148, doi:10.3847/1538-4357/ab2fce, ISSN 0004-637X, Bibcode: 2019ApJ...882..148G 
  7. ↑ 7.0 7.1 7.2 da Silva, Ronaldo; Milone, André de C.; Rocha-Pinto, Helio J. (2015-08-01), "Homogeneous abundance analysis of FGK dwarf, subgiant, and giant stars with and without giant planets", Astronomy and Astrophysics 580: A24, doi:10.1051/0004-6361/201525770, ISSN 0004-6361, Bibcode: 2015A&A...580A..24D  Epsilon Cygni's database entry at VizieR.
  8. ↑ 8.0 8.1 Rumrill, H. B. (1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific 48 (283): 139. doi:10.1086/124681. Bibcode: 1936PASP...48..139R. 
  9. ↑ "LHS 5358b -- High proper-motion Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Epsilon+Cygni, retrieved 2011-12-10 
  10. ↑ 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].
  11. ↑ Allen, Richard Hinckley (1899), "Star-names and their meanings", New York (G.E. Stechert): 197, Bibcode: 1899sntm.book.....A, https://books.google.com/books?id=5xQuAAAAIAAJ&pg=PA197 
  12. ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  13. ↑ "WG Triennial Report (2015-2018) - Star Names". p. 5. https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf. 
  14. ↑ Naming Stars, IAU.org, https://www.iau.org/public/themes/naming_stars/, retrieved 16 December 2017 
  15. ↑ (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.
  16. ↑ (in 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.
  17. ↑ 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, doi:10.1086/133105, Bibcode: 1992PASP..104.1173M 
  18. ↑ Kaler, James, "GIENAH CYGNI (Epsilon Cygni)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/gienahcyg.html, retrieved 2011-12-11 
  19. ↑ Washington Double Star Catalog, United States Naval Observatory, http://ad.usno.navy.mil/wds/, retrieved 2 January 2018 
  20. ↑ 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, doi:10.1086/300813, Bibcode: 1999AJ....117.1864C 
  21. ↑ "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 
  22. ↑ 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, http://www.astro.utoronto.ca/~garrison/mkstds.html, retrieved 2012-02-04 



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