Zeta Aquilae, or ζ Aquilae, is a

binary star A binary star 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 using a telescope as separate stars, in wh ...

system in the equatorial

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 origins of the e ...

of Aquila. It is readily visible with the naked eye, being of the third magnitude. Based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements obtained during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

mission, it is approximately distant from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. It is a candidate member of the

TW Hydrae association The TW Hydrae association is a group of very young low-mass stars and substellar objects located approximately 25–75 parsecs (80–240 light years) from Earth. They share a common motion and appear to all be roughly the same age, 10±3 million yea ...

of co-moving stars. Zeta Aquilae's two components can be designated Zeta Aquilae A (officially named Okab , the traditional name for the system) and B. Zeta Aquilae has a number of companions listed and together they are designated WDS J19054+1352. As the primary star of this group, Zeta Aquilae also bears the designation WDS J19054+1352A. The companions are then designated WDS J19054+1352B, C, D and E.

Nomenclature

''ζ Aquilae'', Latinised to ''Zeta Aquilae'', is the binary's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. The designations of the two components as ''Zeta Aquilae A'' and ''B'' 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. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

s, and adopted by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(IAU). WDS J19054+1352 is the entry of the wider system of which Zeta Aquilae is a member in the

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141, ...

. Zeta and Epsilon Aquilae together bore the traditional name ''Deneb el Okab'', from an

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

term ذنب العقاب ''Dhanab al-ʽuqāb'' "the tail of the eagle", which they mark (''Aquila'' is

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for 'eagle'). 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 ''Okab'' for the component Zeta Aquilae A on 1 June 2018 and it is now so included in the List of IAU-approved Star Names. Epsilon and Zeta Aquilae also bore the

Mandarin Mandarin or The Mandarin may refer to: Language * Mandarin Chinese, branch of Chinese originally spoken in northern parts of the country ** Standard Chinese or Modern Standard Mandarin, the official language of China ** Taiwanese Mandarin, Stand ...

names ''Woo'' and ''Yuë'' , derived from and representing the old states '' Wú'' (吳) (located at the mouth of the

Yangtze River The Yangtze or Yangzi ( or ; ) is the longest list of rivers of Asia, river in Asia, the list of rivers by length, third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in th ...

) and '' Yuè'' (越) (in

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by Jiang ...

province). In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', Zeta Aquilae was designated ''Dzeneb al Tair'' (from the Arabic ذنب الطائر ''ðanab aṭ-ṭā’ir''), which was translated into Latin as ''Cauda (Vulturis) Volantis'', meaning ''the eagle's tail''. In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

, (), meaning '' Left Wall of Heavenly Market Enclosure'', refers to an asterism which represents eleven old states in China and is marking the left borderline of the enclosure, consisting of Zeta Aquilae;

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D ( NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also ...

Lambda Lambda (}, ''lám(b)da'') is the 11th letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoenician Lamed . Lambda gave rise ...

, Mu,

Omicron Omicron (; uppercase Ο, lowercase ο, ell, όμικρον) is the 15th letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the close-mid back rounded vowel in contras ...

and 112 Herculis; Theta¹ and

Eta Serpentis Eta Serpentis, Latinized from η Serpentis, is a star in the constellation Serpens. In particular, it lies in Serpens Cauda, the snake's tail. The star has an apparent visual magnitude of 3.260, making it visible to the naked eye. Par ...

;

Nu Ophiuchi Nu Ophiuchi (ν Oph, ν Ophiuchi) is a star in the equatorial constellation of Ophiuchus. The apparent visual magnitude is +3.3, making it one of the brighter members of this constellation. Based upon parallax measurements made during ...

Xi Serpentis Xi Serpentis, Latinized from ξ Serpentis, is a triple star system in the Serpens Cauda (tail) section of the equatorial constellation Serpens. Based upon an annual parallax shift of 30.98 mas as seen from Earth, it is located 105 ...

and

Eta Ophiuchi Eta Ophiuchi (η Ophiuchi, abbreviated Eta Oph, η Oph) is a binary star in the constellation of Ophiuchus. Based on stellar parallax, parallax measurements taken during the Hipparcos mission, it is approximately 88 light-years from the ...

. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are often a ...

for Zeta Aquilae itself is (, en, the Sixth Star of Left Wall of Heavenly Market Enclosure), representing the state mentioned above.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.

Properties

The primary, designated component A, has 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 grati ...

of A0 Vn, with the

luminosity class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

'V' indicating is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star that is generating energy through the

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...

of hydrogen at its core. It has more than double

the mass Mass is the main Eucharistic liturgical service in many forms of Western Christianity. The term ''Mass'' is commonly used in the Catholic Church, in the Western Rite Orthodox, in Old Catholic, and in Independent Catholic churches. The term is ...

and twice the radius of the

, and is radiating more than 39 times the Sun's luminosity. 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 the star's outer envelope is about 9620 K, which gives it the white hue typical of

A-type star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

s. The estimated age of this star is 50–150 million years. This star is rotating rapidly, with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of 317 km s⁻¹ giving a lower bound on the

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

al velocity along the equator. As a result, it has a pronounced equatorial bulge, causing the star to assume an

oblate spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has circ ...

al shape. The equatorial radius is about 30.7% greater than the polar radius. Because of the

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

, this rapid rotation makes the

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s in the star's

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

broaden and smear out, as indicated by the 'n' suffix in the stellar class. Astronomers use Zeta Aquilae as a telluric standard star. That is, the spectrum of this star is used to correct for

telluric contamination Telluric contamination is contamination of the astronomical spectra by the Earth's atmosphere. Interference with astronomical observations Most astronomical observations are conducted by measuring photons ( electromagnetic waves) which originate ...

from the Earth's atmosphere when examining the spectra of neighboring stars. Observation of this star in the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

band during the

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

survey appeared to reveal excess emission. However, the distribution of this emission couldn't be readily explained by a conjectured disk of circumstellar dust. Instead, the detection was later ascribed to errors caused by saturation of the near-infrared detectors.

Companions

The primary forms a binary star system with component B. This is a magnitude 12.0 star at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the d ...

of 46°, as of 2009. The pair have a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

of . The secondary has an estimated mass equal to one half the mass of the Sun. The 16th magnitude star WDS J19054+1352E is also considered to be a co-moving companion with a mass of , at a projected separation of from the primary. The

lists a second 12th magnitude star at 160" (WDS J19054+1352C) plus an 11th magnitude star separated by 200" (WDS J19054+1352D). The

Catalog of Components of Double and Multiple Stars The Catalog of Components of Double and Multiple Stars, or CCDM, is an astrometric star catalogue of double and multiple stars. It was made by Jean Dommanget and Omer Nys at the Royal Observatory of Belgium in order to provide an input cata ...

lists the two 12th magnitude companions at 6.5" and 160".

References

External links

Image Zeta Aquilae
{{DEFAULTSORT:Zeta Aquilae A-type main-sequence stars Binary stars Aquila (constellation) Aquilae, Zeta BD+13 3899 Aquilae, 17 4095 177724 093747 7325 Okab