Alpha Arae
Encyclopedia
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Alpha Arae (α Arae, α Ara) is the second brightest star
in the constellation
Ara
.
With β
and σ Ara
it forms the Chinese asterism
Choo （pinyin
: chǔ, ）, "pestle" in traditional Chinese astronomy
. It was the second star of Choo （）, but R. H. Allen used the name Choo for this star only. Patrick Moore
lists Choo as a proper name for this star in his star catalogue
of the constellation Ara. This name is also spelt Tchou. There is another Choo in the constellation Pegasus
.
In Chinese
, , meaning Pestle
, refers to an asterism consisting of α Arae, σ Arae
and β Arae
. Consequently, α Arae itself is known as
It is a variable
Be star
approximately 240 light-years from the Earth
, with an apparent visual magnitude which varies between 2.76m and 2.90m.
Like other Be stars, Alpha Arae rotates quickly, rapidly enough in fact to be surrounded by a equatorial disk of material ejected from the star. In 2003 and 2005, Alpha Arae was observed by infrared
interferometry
, using the MIDI and AMBER instruments at the VLT Interferometer. The results, published in 2005 and 2007, appear to show that Alpha Arae has an equatorial rotational speed of about 470 km/s
, that it is surrounded by a dense equatorial disk of material in Keplerian (rather than uniform) rotation, and that it is losing mass by a polar stellar wind
with a terminal velocity of approximately 1,000 km/s. There is also some evidence that Alpha Arae is orbited by a companion at 0.7 AU.
, CCDM J17318-4953B, located approximately 50 arcseconds away, with an apparent visual magnitude of about 11. The two stars appear close to each other by coincidence and are not physically close in space.
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name...
}}
Alpha Arae (α Arae, α Ara) is the second brightest star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Ara
Ara (constellation)
Ara is a southern constellation situated between Scorpius and Triangulum Australe. Its name is Latin for "altar". Ara was one of the 48 Greek constellations described by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations defined by the International Astronomical...
.
With β
Beta Arae
Beta Arae is the brightest star in the constellation Ara.Beta Arae is an orange K-type bright giant or supergiant with an apparent magnitude of +2.84...
and σ Ara
Sigma Arae
Sigma Arae is a star in the constellation Ara. It is a white A-type main sequence dwarf with an apparent magnitude of +4.56. It is approximately 386 light years from Earth.-References:* *...
it forms the Chinese asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
Choo （pinyin
Pinyin
Pinyin is the official system to transcribe Chinese characters into the Roman alphabet in China, Malaysia, Singapore and Taiwan. It is also often used to teach Mandarin Chinese and spell Chinese names in foreign publications and used as an input method to enter Chinese characters into...
: chǔ, ）, "pestle" in traditional Chinese astronomy
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
. It was the second star of Choo （）, but R. H. Allen used the name Choo for this star only. Patrick Moore
Patrick Moore
Sir Patrick Alfred Caldwell-Moore, CBE, FRS, FRAS is a British amateur astronomer who has attained prominent status in astronomy as a writer, researcher, radio commentator and television presenter of the subject, and who is credited as having done more than any other person to raise the profile of...
lists Choo as a proper name for this star in his star catalogue
Star catalogue
A star catalogue, or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some...
of the constellation Ara. This name is also spelt Tchou. There is another Choo in the constellation Pegasus
Pegasus (constellation)
Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
.
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Pestle
Winnowing Basket (Chinese constellation)
The Winnowing Basket mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the eastern mansions of the Azure Dragon.-Asterisms:...
, refers to an asterism consisting of α Arae, σ Arae
Sigma Arae
Sigma Arae is a star in the constellation Ara. It is a white A-type main sequence dwarf with an apparent magnitude of +4.56. It is approximately 386 light years from Earth.-References:* *...
and β Arae
Beta Arae
Beta Arae is the brightest star in the constellation Ara.Beta Arae is an orange K-type bright giant or supergiant with an apparent magnitude of +2.84...
. Consequently, α Arae itself is known as
It is a variable
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
Be star
Be star
A Be star is a B-type star with prominent emission lines of hydrogen in its spectrum. The designation is combined by the spectral class, B, and the lowercase e denoting emission in the spectral classification system. Line emission from other atomic ions might be present as well, but is typically...
approximately 240 light-years from the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, with an apparent visual magnitude which varies between 2.76m and 2.90m.
Like other Be stars, Alpha Arae rotates quickly, rapidly enough in fact to be surrounded by a equatorial disk of material ejected from the star. In 2003 and 2005, Alpha Arae was observed by infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
, using the MIDI and AMBER instruments at the VLT Interferometer. The results, published in 2005 and 2007, appear to show that Alpha Arae has an equatorial rotational speed of about 470 km/s
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
, that it is surrounded by a dense equatorial disk of material in Keplerian (rather than uniform) rotation, and that it is losing mass by a polar stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...
with a terminal velocity of approximately 1,000 km/s. There is also some evidence that Alpha Arae is orbited by a companion at 0.7 AU.
Visual companion
The Be star described above has a visual companion starDouble star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
, CCDM J17318-4953B, located approximately 50 arcseconds away, with an apparent visual magnitude of about 11. The two stars appear close to each other by coincidence and are not physically close in space.
See also
- Traditional Chinese star names in Ara
- Traditional Chinese star names in Pegasus
External links
- HR 6510, entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDSCentre de Données astronomiques de StrasbourgThe Centre de données astronomiques de Strasbourg is a data hub which collects and distributes astronomical information. It was established in 1972 under the name Centre de Données Stellaires...
ID V/50. - Image of Alpha Arae from AladinAladin Sky AtlasAladin is an interactive software sky atlas allowing the user to visualize digitized astronomical images, superimpose entries from astronomical catalogues or databases, and interactively access related data and information from the SIMBAD database, the VizieR service and other archives for all...
.