Epsilon Cygni
Template:Short description Template:Starbox begin Template:Starbox image Template:Starbox observe Template:Starbox character Template:Starbox astrometry Template:Starbox orbit Template:Starbox detail Template:Starbox catalog Template:Starbox reference Template:Starbox end 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.
The system has two confirmed constituents, Epsilon Cygni Aa (officially named Aljanah Template:IPAc-en) and Ab. Additionally, a visual companion (Epsilon Cygni C) is likely bound to the system.<ref name=Heeren2021/>
NomenclatureEdit
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).<ref name="planetnaming">Template:Cite arXiv</ref>
Epsilon Cygni bore the traditional name Gienah from the Arabic al janāħ (Template:Langx) meaning "the wing".<ref name="hinkley1899" /> However that name was more usually applied to Gamma Corvi.<ref name="rumrill" /> For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized a Working Group on Star Names (WGSN)<ref name="WGSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.<ref name="TriRpt18">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name="IAU-LSN" />
In Chinese astronomy, the "Celestial Ford" (Template:Zh) 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.<ref name="G1zAz">Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.</ref> Consequently, the Chinese name for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" (Template:Zh).<ref name="5g83o">Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>
CompanionsEdit
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.<ref name="pasp104_682_1173" /> 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.<ref name="kaler" />
PropertiesEdit
Epsilon Cygni A is a single-lined spectroscopic binary.<ref name="WDS" /> 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.<ref name=Heeren2021/>Template:Efn Its main component is a giant star with a stellar classification of K0 III.<ref name="aj117_4_1864" /> 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.<ref name=Heeren2021/> The effective temperature of its photosphere is 4,700 K,<ref name=Gray2019/> giving an orange hue that is a characteristic of K-type stars.<ref name="csiro" /> Being 10% more massive than the Sun and nine billion years old,<ref name=Heeren2021/> It has 11 times the radius of the Sun<ref name=Gray2019/> and is about 56 times more luminous.<ref name="da Silva"/>
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 Template:Solar mass.<ref name=Heeren2021/>
Since 1943, the spectrum of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.<ref name="baas25_1319" />
Veil NebulaEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} 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.
NotesEdit
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