Summary
Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is 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.
  | |
| 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 | |
| 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 mas[1] |
| Distance | 72.7 ± 0.2 ly (22.29 ± 0.06 pc) |
| Absolute magnitude (MV) | +0.74 ± 0.02[4] |
| Orbit[3] | |
| Primary | ε Cyg Aa |
| Companion | ε Cyg Ab |
| Period (P) | 53.693+0.321 −0.328 yr |
| Semi-major axis (a) | 15.8±0.2 AU |
| Eccentricity (e) | 0.9295±0.0003 |
| Argument of periastron (ω) (primary) | 275.30±0.06° |
| Semi-amplitude (K1) (primary) | 4.6 km/s |
| Details | |
| A | |
| Mass | 1.103±0.042[3] M☉ |
| Radius | 11.13[6] R☉ |
| Luminosity | 56.4±0.6[7] L☉ |
| Surface gravity (log g) | 2.79±0.23[7] cgs |
| Temperature | 4,699[6] K |
| Metallicity [Fe/H] | −0.126[6] dex |
| Rotation | 0.67[4] years |
| Rotational velocity (v sin i) | 2.3 ± 0.2[4] km/s |
| Age | 9.62±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 | |
| SIMBAD | data |
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
editε 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
editEpsilon 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
edit
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][a] 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
editε 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
edit- ^ 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
edit- ^ a b c d e 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.
- ^ a b c 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
- ^ a b c d e f g h i j Heeren, Paul; Reffert, Sabine; Trifonov, Trifon; Wong, Ka Ho; Lee, Man Hoi; Lillo-Box, Jorge; Quirrenbach, Andreas; Arentoft, Torben; Albrecht, Simon; Grundahl, Frank; Andersen, Mads Fredslund; Antoci, Victoria; Pallé, Pere L. (2021-03-01), "Precise radial velocities of giant stars - XV. Mysterious nearly periodic radial velocity variations in the eccentric binary ε Cygni", Astronomy & Astrophysics, 647: A160, arXiv:2102.01999, Bibcode:2021A&A...647A.160H, doi:10.1051/0004-6361/202040087, ISSN 0004-6361
- ^ a b c d 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. S2CID 125700196.
- ^ 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
- ^ a b c d e 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, Bibcode:2019ApJ...882..148G, doi:10.3847/1538-4357/ab2fce, ISSN 0004-637X
- ^ a b c 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, arXiv:1505.01726, Bibcode:2015A&A...580A..24D, doi:10.1051/0004-6361/201525770, ISSN 0004-6361 Epsilon Cygni's database entry at VizieR.
- ^ a b 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. S2CID 120743052.
- ^ "LHS 5358b -- High proper-motion Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-10
- ^ 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].
- ^ Allen, Richard Hinckley (1899), "Star-names and their meanings", New York, G.E. Stechert: 197, Bibcode:1899sntm.book.....A
- ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
- ^ "Naming Stars". IAU.org. Retrieved 16 December 2017.
- ^ (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.
- ^ (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.
- ^ 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
- ^ Kaler, James, "GIENAH CYGNI (Epsilon Cygni)", Stars, University of Illinois, retrieved 2011-12-11
- ^ "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 14 February 2011. Retrieved 2 January 2018.
- ^ 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
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
- ^ 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, archived from the original on 2019-06-25, retrieved 2012-02-04
External links
edit- http://www.pbase.com/mcrowle/image/81902791