Eta Aquilae (η Aql, η Aquilae) is the

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. ...

for a multiple star 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 ...

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 ...

, the eagle. It was once part of the former 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 ...

. On average, this star has an apparent visual magnitude of 3.87, making it one of the brighter members of Aquila. 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 made 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, this star is located at a distance of roughly , although the parallax estimate has a 44% margin of error.

System

The η Aquilae system contains at least two stars, probably three. The primary star η Aql A is by far the brightest and dominates the spectrum. An ultraviolet excess in the spectral energy distribution suggest the presence of a faint hot companion, η Aql B, which has been given a spectral type of B8.9 V. The fractional spectral type is an artefact of the mathematics used to model the spectrum, not an indication of any specific spectral features that would be intermediate between B8 and B9. Radial velocity measurements could not find a satisfactory fit, which suggests that the orbit of η Aql B may be face-on, or very large. A companion has been resolved visually 0.66" distant, but measurements give this a spectral type of F1 - F5. It seems likely that the hot star detected in the spectrum is closer and unresolved. The resolved companion has not been shown to be physically associated, but it is estimated that it would have a period of nearly a thousand years. Measurements with the HST fine guidance sensors show variations likely to be due to orbital motion on a scale of two years, so η Aql would appear to be a triple system.

Cepheid Variable

η Aquilae A is a Cepheid variable star, discovered by Edward Pigott in 1784. It has an apparent magnitude that ranges from 3.5 to 4.3 over a period of 7.176641 days. Along with

Delta Cephei Delta Cephei (δ Cep, δ Cephei) is the Bayer designation for a quadruple star system located approximately 887 light-years away in the northern constellation of Cepheus, the King. At this distance, the visual magnitude of the star is ...

, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids; that is, both the star itself and the variation in its brightness can be distinguished with the naked eye. Some other Cepheids such as

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...

are bright but have only a very small variation in brightness. At the relatively young age of 26 million years, this massive star has burned through the hydrogen fuel at its core and evolved into a supergiant, giving it a baseline

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 F6 Ibv. The periodic pulsations of this star actually cause the stellar class to vary between (F6.5–G2)Ib over the course of each cycle. Compared to the Sun, Eta Aquilae has around 9 times the mass, roughly 66 times the radius, and is radiating 11,474 times as much luminosity. This energy is being emitted from the outer envelope 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 6,000 K, giving it the yellow-white hued glow of an F-type star. The radius of the star varies by () over the course of a pulsation cycle. Compared to its neighbors, this star has a high peculiar velocity of .

Name

In Chinese, (), meaning '' Celestial Drumstick'', refers to an asterism consisting of η Aquilae, θ Aquilae,

62 Aquilae 62 Aquilae is a single star located about 427 light years away from the Sun in the equatorial constellation of Aquila. ''62 Aquilae'' is its Flamsteed designation. It is visible to the naked eye as a dim, orange-hued star with an app ...

and

58 Aquilae 58 Aquilae is a single star located around 520 light years from the Sun in the celestial equator, equatorial constellation of Aquila (constellation), Aquila, near Eta Aquilae. ''58 Aquilae'' is its Flamsteed designation. It is visible ...

. Consequently, the Chinese name for η Aquilae itself is (, en, the Fourth Star of Celestial Drumstick.)AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
/ref> This star, along with δ 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'' was the title for three stars: δ Aql as ''Al Mizān I'', η Aql as ''Al Mizān II'' and θ Aql as ''Al Mizān III''. η Aquilae, together with θ Aql, δ Aql, ι Aql, κ Aql and λ Aql, was part of the obsolete constellation

References

External links

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Eta Aquilae

Image Eta Aquilae
{{DEFAULTSORT:Eta Aquilae Al Mizān II 187929 Aquila (constellation) Aquilae, Eta Classical Cepheid variables F-type supergiants F-type main-sequence stars B-type main-sequence stars Triple star systems Aquilae, 55 7570 097804 J19522835+0100203 BD+00 4337