ε Cygni
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Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is a
binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
in the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...
of Cygnus. With an
apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...
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 Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
measurement, Epsilon Cygni is about 73
light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s distant. The system has two confirmed constituents, Epsilon Cygni Aa (officially named Aljanah ) and Ab. Additionally, a visual companion (Epsilon Cygni C) is likely bound to the system.


Nomenclature

''ε Cygni'' ( Latinised to ''Epsilon Cygni'') is the system's
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
. 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 system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...
s, and adopted by the
International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
(IAU). Epsilon Cygni bore the traditional name ''Gienah'' from the
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
''al janāħ'' () meaning "the
wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...
". However that name was more usually applied to
Gamma Corvi Gamma Corvi (γ Corvi, abbreviated Gamma Crv, γ Crv) is a binary star and the brightest star in the southern constellation of Corvus, having an apparent visual magnitude of 2.59. The system's two components are designated Gamma Corvi A (o ...
. For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized a
Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. 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. In
Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The Ancient China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...
, the " Celestial Ford" () refers to an asterism consisting of Epsilon Cygni,
Gamma Cygni Gamma Cygni is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. It is officially named Sadr , gamma Cygni is its Bayer designation, which that is Latiniz ...
,
Delta Cygni Delta Cygni is a binary star of a combined third-magnitude in the constellation of Cygnus (constellation), Cygnus. It is also part of the Northern Cross (asterism), Northern Cross Asterism (astronomy), asterism whose brightest star is D ...
,
30 Cygni 30 Cygni (ο1 Cygni) is a class A5III (white giant) star in the constellation Cygnus. Its apparent magnitude is 4.83 and it is approximately 610 light years away based on parallax. The Bayer letter ο (omicron) has been variously appli ...
, Alpha Cygni,
Nu Cygni Nu Cygni, Latinized from ν Cygni, is a binary star system in the constellation Cygnus. Its apparent magnitude is 3.94 and it is approximately 374 light years away based on parallax. The brighter component is a magnitude 4.07 A-type g ...
,
Tau Cygni Tau Cygni, Latinised from τ Cygni, is a binary star system in the constellation Cygnus, approximately 69 light years away from Earth. This visual binary system has a period of 49.6 years. The main star, 4th magnitude GJ 822.1 A, is a ...
,
Upsilon Cygni Upsilon Cygni is a star in the northern constellation of Cygnus. Its name is a Bayer designation that is Latinized from υ Cygni, and abbreviated Upsilon Cyg or υ Cyg. It is visible to the naked eye, having an apparent visual magnitude ...
and Zeta Cygni. ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, the
Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...
for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" ().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.


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 Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...
companion, Epsilon Cygni C, at an angular separation of 78
arcseconds A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
. If the latter star is
gravitationally bound The gravitational binding energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. A gravitationally bound system has a lower (''i.e.'', more negative) gravitatio ...
to Epsilon Cygni A, then they are currently separated by 1,700  AU or more, and have an
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
of at least 50,000 years.


Properties

Epsilon Cygni A is a single-lined spectroscopic binary. The components take 53 years to complete an orbit and are in a highly eccentric orbit, which put their distances from 1.1 
astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s in
apoapsis An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...
to 30.5 astronomical units in
periapsis An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...
. Its main component is a
giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...
with a
stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...
of K0 III. This indicates that the star has left the
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
and has begun the final stages in its
stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...
. After passing through the 
red-giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass st ...
 stage, it underwent a 
helium flash A helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low-mass stars (between 0.5-0.44 solar masses () and 2.0 ) during their red giant phase. The Su ...
event and is now a 
horizontal branch The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha proc ...
star generating energy through the 
thermonuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...
 of helium at its
core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (laboratory), a highly specialized shared research resource * Core (manufacturing), used in casting and molding * Core (optical fiber ...
. The
effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
of its
photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
is 4,700 K, giving an orange hue that is a characteristic of K-type stars. Being 10% more massive than the Sun and nine billion years old, It has 11 times the
radius of the Sun Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...
and is about 56 times more luminous. The secondary has never been observed directly, its existence was inferred solely on
astronomical spectroscopy Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the electromagnetic spectrum, spectrum of electromagnetic radiation, including Visible light astronomy, visible light, Ultraviolet astronomy, ultr ...
. Based on this data, it should have a mass of at least . Since 1943, the
spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.


Veil Nebula

ε Cygni lies about three degrees north of the
Veil nebula The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus. It constitutes the visible portions of the Cygnus Loop, a supernova remnant, many portions of which have acquired their own individual names and cat ...
, a probable ancient
supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
. The nebula is far more distant than the star.


Notes


References


External links

* http://www.pbase.com/mcrowle/image/81902791 {{Stars of Cygnus Cygni, Epsilon Cygnus (constellation) K-type giants Aljanah Cygni, 53 7949 197989 102488 BD+33 4018 0806.1 Multiple stars Horizontal-branch stars