Xi Aquilae (ξ Aquilae, abbreviated Xi Aql, ξ Aql), officially named Libertas , is a red-clump giant star located at a distance of from the Sun 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 ...

. As of 2008, an extrasolar planet (designated Xi Aquilae b, later named Fortitudo) has been confirmed in orbit around the star.

Nomenclature

''ξ Aquilae'' ( Latinised to ''Xi Aquilae'') is the star'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. ...

. Following its discovery the planet was designated Xi Aquilae b. In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning names were Libertas for this star and Fortitudo for its planet. The winning names were those submitted by Libertyer, a student club at Hosei University of Tokyo,

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. The names which were originally proposed were in English and were 'Liberty' and 'Fortitude', but to comply with the IAU's rules they were modified to be Latin versions of the same words, and so the final names became 'Libertas' and 'Fortitudo' respectively. 'Aquila' is Latin for '

eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...

', a popular symbol of liberty and embodiment of fortitude—emotional and mental strength in the face of adversity.NameExoWorlds The Approved Names
/ref> In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. In its first bulletin of July 2016, the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.

Properties

This star has an apparent visual magnitude of 4.722, which, according to the Bortle Dark-Sky scale, is bright enough to be viewed with the naked eye from dark suburban skies. The orbital motion of the Earth causes this star to undergo an annual

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 ...

shift of 17.77 milliarcseconds. From this measurement, the distance to this star can be determined, yielding an estimate of approximately 184 light-years with a 2% margin of error. The magnitude of the star is diminished by 0.09 from the extinction caused by interstellar gas and dust. The spectrum of this star is considered a standard example of the

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 ...

G9.5 IIIb, where the G9.5 means that it belongs to the category of G-type stars while the luminosity class of IIIb indicates that, at an estimated age of nearly five billion years, is an

evolved star 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 cons ...

that has reached the giant stage. It is in the red clump, meaning it is generating energy through the fusion of helium into carbon at its core. Xi Aquilae has an estimated 116% of the Sun's mass, while its outer atmosphere has expanded to more than ten times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars 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_ = 6.9 ...

. It is radiating 49 times the Sun's luminosity 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 golden-hued glow of a G-type star. The possibility of a binary stellar companion can be ruled out based upon observations with the CHARA array.

Planetary system

In 2008, the presence of a planetary companion was announced, based upon Doppler spectroscopy results from the

Okayama Astrophysical Observatory The (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii and Chile. It was established in 1988 as an amalgamation of three existing research organizations - the Tokyo Astro ...

. This object, designated as

Xi Aquilae b Xi Aquilae b (abbreviated ξ Aquilae b, ξ Aql b), formally named Fortitudo , is an extrasolar planet approximately 200 light-years from the Sun in the constellation of Aquila. The planet was discovered orbiting the yellow giant star Xi Aquilae ...

, has at least 2.8 Jupiter masses and is orbiting at an estimated 0.68 astronomical unit from the star with a period of 136.75 days. Any planets that once orbited to the interior of this object may have been consumed as the star entered the

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

stage and expanded in radius.

References

External links

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HR 7595

Image Xi Aquilae

wikisky.org
{{DEFAULTSORT:Xi Aquilae G-type giants Horizontal-branch stars Planetary systems with one confirmed planet Aquila (constellation) Libertas Aquilae, Xi Durchmusterung objects Aquilae, 59 188310 097938 7595