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 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 speaking, ...

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 ...

of Aquila, 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 Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

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 The margin of error is a statistic expressing the amount of random sampling error in the results of a survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of a census of the e ...

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 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 ...

. An

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

excess in the

spectral energy distribution A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astron ...

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 A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid varia ...

star, discovered by

Edward Pigott Edward Pigott (1753–1825) was an English astronomer notable for being one of the founders of the study of variable stars. Biography Son of the astronomer Nathaniel Pigott, Pigott's work focused on variable stars. Educated in France wit ...

in 1784. It has an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

that ranges from 3.5 to 4.3 over a period of 7.176641 days. Along with Delta Cephei,

Zeta Geminorum Zeta Geminorum (ζ Geminorum, abbreviated Zeta Gem, ζ Gem) is a bright star with cluster components, distant optical components and a likely spectroscopic partner in the zodiac constellation of Gemini — in its south, on the left 'le ...

and

Beta Doradus Beta Doradus, Latinized from β Doradus, is the second brightest star in the southern constellation of Dorado. It has a variable apparent visual magnitude, and is visible to the naked eye from the southern hemisphere. Based upon parallax ...

, it is one of the most prominent

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

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 Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

into a

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

, 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 An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

. 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 Peculiar motion or peculiar velocity refers to the velocity of an object relative to a ''rest frame'' — usually a frame in which the average velocity of some objects is zero. Galactic astronomy In galactic astronomy, peculiar motion refers to ...

of .

Name

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 '' Celestial Drumstick'', refers to an asterism consisting of η Aquilae, θ Aquilae, 62 Aquilae 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 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 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