Epsilon Sagittarii ( Latinised from ε Sagittarii, abbreviated Epsilon Sgr, ε Sgr), formally named Kaus Australis , is a

binary star A binary star or binary star system 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 as separate stars us ...

system in the southern

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the Sun across the celestial sphere over the course of the year. Within this 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 first constellati ...

of Sagittarius. The

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

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 sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements, this star is around from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

Observation

Epsilon Sagittarii can best be viewed in the month of August. The star is at least 10 degrees away from the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

, and the

passes it overhead around December 25-26th. The star is visible from late January to late November from mid-northern latitudes. From mid-southern latitudes, the star is visible from early January until the middle of December. The star is not visible in areas above 55°N latitude. From latitudes below 55°S, Epsilon Sagittarii is a

circumpolar star A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest p ...

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 gratin ...

of B9.5IVp, with the

luminosity class 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 gratin ...

of IV suggesting it has a

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

comparable to a

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

for its spectral type. It is suggested that chemical peculiarities in the spectrum may indicate a

λ Boötis star Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoeni ...

. It has about 3.8 times the

mass of the Sun The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and is radiating around 500 times the

Sun's luminosity The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

from its

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

. Epsilon Sagittarii A is spinning rapidly with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 236 km s⁻¹. This rapid rotation give the star an oblate shape, with its equatorial circumference being 34% larger than its polar circumference. The

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 ...

across the star's surface varies as well, from 7,433K in the equator to 11,720K in the poles. At its equator, it is rotating at 95% of its critical (breakup) velocity, the highest rate ever measured for a star in the Milky Way. It also possesses a gaseous equatorial

decretion disk Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

. Its unusually rapid rotation is incompatible with

stellar evolution 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 consi ...

models, and thus Epsilon Sagittarii is more likely the result of mass transfer of two stars previously in a binary system. It has a magnetic field with a strength in the range 10.5–130.5

Gauss Johann Carl Friedrich Gauss (; ; ; 30 April 177723 February 1855) was a German mathematician, astronomer, Geodesy, geodesist, and physicist, who contributed to many fields in mathematics and science. He was director of the Göttingen Observat ...

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 would suggest the presence of a circumstellar disk of dust, but these claims were later found to be doubtful.

Companion stars

As of 2001, the secondary star, ε Sagittarii B, is located at an

angular separation Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

of 2.392

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

s from the primary along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...

of 142.3°. At the distance of this system, this angle is equivalent to a physical separation of about 106 AU. It is likely to be a

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

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, but a more recent analysis suggest that it is caused by the presence of a gas disk around the primary. Prior to its 1993 identification using an

adaptive optics Adaptive optics (AO) is a technique of precisely deforming a mirror in order to compensate for light distortion. It is used in Astronomy, astronomical telescopes and laser communication systems to remove the effects of Astronomical seeing, atmo ...

coronagraph A coronagraph is a telescopic attachment designed to block out the direct light from a star or other bright object so that nearby objects – which otherwise would be hidden in the object's bright glare – can be resolved. Most coronagr ...

, this companion may have been responsible for the spectral anomalies that were attributed to the primary star. At least two further companions have been listed for Epsilon Sagittarii. There is a 14th-magnitude star (UCAC3 112-415471) at an angular separation of 32.3 arcseconds, but it has a much smaller parallax and so is likely to be a background object. HD 169178 is a 9th-magnitude star separated from Epsilon Sagittarii by ; it has a similar parallax and proper motion and is listed in the

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of January 2024) 1 ...

as a companion.

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 alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. It bore the traditional name ''Kaus Australis'', which derived from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

قوس ''qaws'' 'bow' and

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''austrālis'' 'southern'. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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 Muḥammad al Achsasi al Mouakket () was a 17th century Egyptian astronomer whose and catalogue of stars, ("''Pearls of brilliance upon the solar operations''"), was written in Cairo in about 1650. Al-Achsasi was a shaykh, a learned elder, of th ...

, this star was designated ''Thalath al Waridah'', or ''Thalith al Waridah'', meaning 'third of Warida'. In

Chinese Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

, (), meaning ''

Winnowing Basket A winnowing basket or fan is a tool for winnowing grain from chaff while removing dirt and dust too. They have been used traditionally in a number of civilizations for centuries, and are still in use today in some countries. Use Unprocessed g ...

'', 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 Delta Sagittarii (δ Sagittarii, abbreviated Delta Sgr, δ Sgr), formally named Kaus Media , is a star in the southern zodiac constellation of Sagittarius. The apparent visual magnitude of this star is +2.70, making it ea ...

and Eta Sagittarii. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Epsilon Sagittarii itself is (, .)AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
This star, together with: *

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 after Kaus Australis and Nunki. Based upon parallax measurements, i ...

Lambda Sagittarii Lambda Sagittarii ( Latinized from λ Sagittarii), formally named Kaus Borealis , is a star in the southern constellation of Sagittarius. The star marks the top of the Archer's bow. Properties With an apparent visual magnitude of ...

Sigma Sagittarii Sigma Sagittarii, Latinized from σ Sagittarii; formally named Nunki , is the second-brightest star in the constellation of Sagittarius. It is a binary star system, viewed as a single star of combined apparent magnitude +2.05, abou ...

Tau Sagittarii Tau Sagittarii (Tau Sgr, τ Sagittarii, τ Sgr) is a star in the southern zodiac constellation of Sagittarius. Description With an apparent visual magnitude of +3.3, this is one of the brighter members of the constellatio ...

and

Phi Sagittarii Phi Sagittarii, Latinized from φ Sagittarii, is a binary 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 ...

, comprise the ''

Teapot A teapot is a vessel used for steeping tea leaves or a herbal mix in boiling or near-boiling water and serving the resulting infusion called tea; usually put in a teacup. It is one of the core components of teaware. Teapots usually have an ...

'' asterism. *

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

and

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 of

Mato Grosso Mato Grosso ( – ) is one of the states of Brazil, the List of Brazilian states by area, third largest by area, located in the Central-West Region, Brazil, Central-West region. The state has 1.66% of the Brazilian population and is responsible ...

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".

Notes

References

External links

Kaus Australis
{{DEFAULTSORT:Epsilon Sagittarii Sagittarii, Epsilon B-type subgiants Binary stars Sagittarius (constellation) Kaus Australis Circumstellar disks Sagittarii, 20 6879 169022 090185 CD-34 12784