Epsilon Sagittarii ( Latinised from ε Sagittarii, abbreviated Epsilon Sgr, ε Sgr), formally named Kaus Australis , 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 southern zodiac

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 Sagittarius. The apparent visual magnitude of +1.85 makes it the brightest object in Sagittarius. 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, this star is around from the Sun.

Stellar system

The primary star, ε Sagittarii A, of this binary star system has 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 B9.5 III, with the luminosity class of III suggesting this is an evolved giant star that has exhausted the supply of hydrogen at its core. The

interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

-measured angular diameter of this star, after correcting for limb darkening, is , which, at its estimated distance, equates to a physical radius of about 6.8 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 ...

. This is a close match to the empirically-determined value of 6.9 solar radii. It has about 3.5 times the mass of the Sun and is radiating around 363 times the Sun's luminosity 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 9,960 K. At this heat, the star glows with a blue-white hue. This star is spinning rapidly with a projected rotational velocity of 236 km s⁻¹. It has a magnetic field with a strength in the range 10.5–130.5 Gauss and it is an X-ray source with a luminosity of about 10³⁰ erg s⁻¹. The system displays an excess emission of infrared radiation, which suggests the presence of a circumstellar disk of dust. Based upon the temperature of this disk, it is orbiting at a mean separation of 155 AU from the primary. As of 2001, the secondary star, ε Sagittarii B, is located at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 2.392

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s from the primary along a position angle of 142.3°. At the distance of this system, this angle is equivalent to a physical separation of about 106 AU, which places it inside the debris disk. It is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star with about 95% of the mass of the Sun. The system has a higher optical linear polarisation than expected for its distance from the Sun; this has been attributed to light scattered off the disk from the secondary. Prior to its 1993 identification using an adaptive optics coronagraph, this companion may have been responsible for the spectral anomalies that were attributed to the primary star. There is a candidate stellar companion at an angular separation of 32.3 arcseconds.

Nomenclature

''ε Sagittarii'' ( Latinised to ''Epsilon Sagittarii'') is the star system'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. ...

. It bore the traditional name ''Kaus Australis'', which derived from the Arabic قوس ''qaws'' 'bow' and Latin ''austrālis'' 'southern'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Kaus Australis'' for the star ε Sagittarii A. In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated ''Thalath al Waridah'', or ''Thalith al Waridah'', meaning 'third of

Warida Warida or Al Warida is an asterism of the Arabs. In the star catalogue of Al Achsasi al Mouakket, four stars are mentioned as belonging to it: Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii and Eta Sagittarii. The name is short for Arabic ...

'. In Chinese, (), meaning '' Winnowing Basket'', refers to an asterism consisting of Epsilon Sagittarii,

Gamma Sagittarii The Bayer designation γ Sagittarii (Gamma Sagittarii) is shared by two stars in the 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, ...

, Delta Sagittarii and

Eta Sagittarii Eta Sagittarii (Eta Sgr, η Sagittarii, η Sgr) is a binary star system in the southern zodiac constellation of Sagittarius. Based upon parallax measurements, it is located at a distance of from Earth. It was formerly k ...

. Consequently, the Chinese name for Epsilon Sagittarii itself is (, en, the Third Star of Winnowing Basket.)AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
/ref> This star, together with: *

, Delta Sagittarii,

Zeta Sagittarii Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr) is a triple star system and the third-brightest star in the constellation of Sagittarius. Based upon parallax measurements, it is about from the Sun. The thre ...

, Lambda Sagittarii,

Sigma Sagittarii Sigma Sagittarii, Latinized from σ Sagittarii; formally named Nunki , is the second-brightest star in the constellation of Sagittarius. It has an apparent magnitude of +2.05, making it readily visible to the naked eye. The distanc ...

, Tau Sagittarii and

Phi Sagittarii Phi Sagittarii, Latinized from φ Sagittarii, is a star in the southern constellation of Sagittarius. With an apparent visual magnitude of 3.17, it is the ninth-brightest star in the constellation and is readily visible to the nak ...

, comprise the '' Teapot'' asterism. *

, Delta Sagittarii and

were ''Al Naʽām al Wārid'' (النعم الوارد), the 'Going Ostriches'. *

and Delta Sagittarii were Akkadian ''Sin-nun‑tu'', or ''Si-nu-nu‑tum'', 'the Swallow'. Kaus Australis is listed in the Babylonian compendium MUL.APIN as MA.GUR₈, meaning "the Bark". The

Kalapalo people The Kalapalo are an indigenous people of Brazil. They are one of seventeen tribal groups who inhabit the Xingu National Park in the Upper Xingu River region of the state of Mato Grosso. They speak the Amonap language, a Cariban language, and ...

Mato Grosso Mato Grosso ( – lit. "Thick Bush") is one of the states of Brazil, the third largest by area, located in the Central-West region. The state has 1.66% of the Brazilian population and is responsible for 1.9% of the Brazilian GDP. Neighboring ...

state in Brazil called this star and λ Scorpii, through ι Scorpii, θ Scorpii, ν Scorpii, υ Scorpii and ρ Scorpii ''Taugi kusugu'', "Taugi's fishing basket".

References

External links

Kaus Australis
{{DEFAULTSORT:Epsilon Sagittarii Sagittarii, Epsilon B-type giants Binary stars Sagittarius (constellation)

Kaus Australis Epsilon Sagittarii ( Latinised from ε Sagittarii, abbreviated Epsilon Sgr, ε Sgr), formally named Kaus Australis , is a binary star system in the southern zodiac constellation of Sagittarius. The apparent visual magnitu ...

Circumstellar disks Sagittarii, 20 6879 169022 090185 CD-34 12784