Delta Aquilae, Latinized from δ 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 Equatorial may refer to something related to: *Earth's equator **the tropics, the Earth's equatorial region **tropical climate *the Celestial equator ** equatorial orbit **equatorial coordinate system ** equatorial mount, of telescopes * 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 ...

Aquila Aquila may refer to: Arts, entertainment, and media * ''Aquila'', a series of books by S.P. Somtow * ''Aquila'', a 1997 book by Andrew Norriss * ''Aquila'' (children's magazine), a UK-based children's magazine * ''Aquila'' (journal), an or ...

. It has an apparent visual magnitude of 3.4 and, based upon

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, is located at a distance of about from Earth. It is drifting closer with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −30 km/s. The system is predicted to come to within of the Sun in around 335,000 years.

Properties

The binary nature of this system was first reported by H. L. Alden at Yale Observatory in 1936. It is an

astrometric binary 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 ...

where the two components orbit each other with a period of 3.422 years and an eccentricity (ovalness) of about 0.36. This is a type of

system where the presence of the secondary component is revealed by its gravitational perturbation of the primary. The individual components have not been resolved with a telescope. The primary member, designated component Aa, is an aging subgiant star 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 grati ...

of F0 IV, where the luminosity class of IV indicates it is in the process of exhausting the supply of hydrogen at its core and evolving into a giant star. The mass of the star is 65% greater than the Sun's and it has expanded to more than double the Sun's radius. It is radiating around 7–8 times the luminosity of the Sun from its outer atmosphere at an

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 , giving it the yellow-white hue of an F-type star. Delta Aquilae A is a Delta Scuti variable that exhibits variations in luminosity caused by pulsations in its outer envelope. It is spinning 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 about . This is a lower bound on the azimuthal velocity along the star's equator. The secondary, component Ab, is a smaller star with about 67% of the Sun's mass and an estimated 61% of the radius of the Sun. It may be a K-type star.

Naming

This star, along with η Aql and θ Aql were ''Al Mizān'' (ألميزان), the Scale-beam. According to the catalogue of stars in the ''Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars'', ''Al Mizān'' were the title for three stars: δ Aql as ''Al Mizān I'', η Aql as ''l Mizān II'' and θ Aql as ''Al Mizān III''. Being the westernmost star of the asterism,

Jim Kaler James Bailey "Jim" Kaler (December 29, 1938 — November 26, 2022) was an American astronomer and science writer. After elementary and high-school education in Albany, New York, Kaler earned his A.B. at the University of Michigan in 1960. He atten ...

has suggested the name ''Almizan Occidental''. On the other hand, Antonín Bečvář includes, with no further explanation, ''Deneb Okab'' in his catalogue, meaning ''the tail of eagle'' in Arabic; however, the star is situated in the centre of the constellation, which is usually identified with the chest, while the stars ε Aql and ζ Aql have been collectively known as Deneb al Okab by Arabian medieval astronomers, which might suggest that Bečvář's assumption was a misnomer. In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated ''Djenubi Menkib al Nesr'' (منكب ألنسر ألخنوبي – ''mankib al-nasr al-janúbii''), which was translated into Latin as ''Australior Humerus Vulturis'', meaning the southern shoulder of the eagle. 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 va ...

, (), meaning '' Right Flag'', refers to an asterism consisting of δ Aquilae, μ Aquilae, σ Aquilae, ν Aquilae, ι Aquilae, 42 Aquilae, HD 184701, κ Aquilae and 56 Aquilae. Consequently, the Chinese name for δ Aquilae itself is (, en, the Third Star of Right Flag).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. This star, together with η Aql, θ Aql, ι Aql, κ Aql and λ Aql, were once part of the now-obsolete constellation

Antinous Antinous, also called Antinoös, (; grc-gre, Ἀντίνοος; 27 November – before 30 October 130) was a Greek youth from Bithynia and a favourite and probable lover of the Roman emperor Hadrian. Following his premature death before his ...

References

External links

*An Atlas of the Universe
Multiple Star Orbits

Image δ Aquilae
{{DEFAULTSORT:Delta Aquilae F-type subgiants Astrometric binaries Aquila (constellation) Aquilae, Delta BD+02 3879 Aquilae, 30 0760 182640 095501 7377 Al Mizān I