Xi Ursae Majoris is a quintuple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...

away 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, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Ursa Major Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa M ...

. It has the traditional name Alula Australis; ''Xi Ursae Majoris'' is the

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 ...

, which is Latinised from ξ Ursae Majoris and abbreviated Xi UMa or ξ UMa. It is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

with a small amplitude. Xi Ursae Majoris is found in the left hind paw of the Great Bear. Xi Ursae Majoris is the second-nearest quintuple system, after

V1054 Ophiuchi V1054 Ophiuchi, together with the star Gliese 643, is a nearby quintuple star system, located in the constellation Ophiuchus at a distance of 21.2 light-years. It consists of five stars, all of which are red dwarfs. The alternative ...

History of observations

Xi Ursae Majoris was found to be a visual

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

in 1780, and in 1804 he presented it as a likely physical

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 ...

based on observed orbital motion. It then became the first visual double star for which an orbit was calculated, when it was computed by Félix Savary in

1828 Events January–March * January 4 – Jean Baptiste Gay, vicomte de Martignac succeeds the Jean-Baptiste de Villèle, Comte de Villèle, as Prime Minister of France. * January 8 – The Democratic Party of the United States is organiz ...

Stellar system

The two main components are yellow

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

s. The brighter component (designated Xi Ursae Majoris A), has a mean

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

of +4.41. The companion star (Xi Ursae Majoris B) has an apparent magnitude of +4.87. The

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of the two stars is 59.84 years. They are currently (2022) separated by 2.3

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, and will widen to a maximum 3.0 arcseconds in 2035. Alula Australis - STF1523AB - HIP 55203

Each component of this double star is itself a single-lined

spectroscopic binary 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 ...

. The orbit of the A pair has been determined from spectroscopy and

speckle interferometry Speckle imaging comprises a range of high-resolution Astrophotography, astronomical imaging techniques based on the analysis of large numbers of short Exposure (photography), exposures that freeze the variation of Astronomical seeing, atmospheri ...

, giving a period of 669 days and an eccentricity of 0.53. B's binary companion (Xi Ursae Majoris Bb) has not been detected visually, but the

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

variations of the spectral lines show a circular orbit with a period of 3.98 days. The masses of both A and B's companions (Ab and Bb) (deduced by the sum total mass of the system minus the likely masses of Aa and Ba determined by their class) indicate that they are probably

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

s, Bb being on the cool end of the M spectrum, not much hotter than a

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

. However, component Ba has been found to be enriched in

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

relative to component Aa, suggesting that its companion Bb may be a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

. In 2012 Wright et al. discovered the fifth component and the first brown dwarf of the system using

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, List of observatory codes, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy Space observatory, space telescope in the Explorers Program launched in December 2009.. . WISE L ...

(WISE) data—a T8.5 brown dwarf WISE J111838.70+312537.9 with angular separation 8.5

arcmin 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 ...

, and the projected physical separation about 4,000 AU.

Variable star

ξ Ursae Majoris is classified as an

RS Canum Venaticorum variable An RS Canum Venaticorum variable is a type of variable star. The variable type consists of close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity. ...

and its brightness varies by 0.01 magnitude. Component B is believed to be the variable star, showing characteristic

emission line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

s in its

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

that are not present for component A.

Nomenclature

''ξ Ursae Majoris'' ( Latinised to ''Xi Ursae Majoris'') is the star's

. It also bore the traditional names ''Alula Australis'' (and erroneously ''Alula Australe''). ''Alula'' (shared with

Nu Ursae Majoris Nu Ursae Majoris (ν Ursae Majoris, abbreviated Nu UMa, ν UMa), formally named Alula Borealis , is a double star in the northern circumpolar constellation of Ursa Major. At an apparent visual magnitude of +3.490, it is br ...

) comes 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 ...

phrase 'the First Spring' and ''Australis'' is

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 ...

for '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 ''Alula Australis'' for this star. 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 '' Three Steps'', refers to an asterism consisting of Xi Ursae Majoris,

Iota Ursae Majoris Iota Ursae Majoris (ι Ursae Majoris, abbreviated Iota UMa, ι UMa), also named Talitha , is a star system in the northern circumpolar constellation of Ursa Major. It has an apparent visual magnitude of 3.14, making it vi ...

Kappa Ursae Majoris Kappa Ursae Majoris (κ Ursae Majoris, abbreviated Kappa UMa, κ UMa) is a binary star in the constellation of Ursa Major. With a combined apparent magnitude of +3.60, the system is approximately 358 light-years from Earth ...

Lambda Ursae Majoris Lambda Ursae Majoris (λ Ursae Majoris, abbreviated Lambda UMa, λ UMa), formally named Tania Borealis , is a star in the northern circumpolar constellation of Ursa Major. Properties This star has an apparent visual magnit ...

, Mu Ursae Majoris and

. 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 Xi Ursae Majoris itself is (, ).(Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日

References

Note

External links

Animation of the orbits of the stars in the Alula Australis System at SolStation.com

by Dr. Jim Kaler. {{Stars of Ursa Major F-type main-sequence stars G-type main-sequence stars M-type main-sequence stars T-type brown dwarfs Ursae Majoris, Xi RS Canum Venaticorum variables Emission-line stars Spectroscopic binaries 5 Ursa Major Ursae Majoris, Xi 4374 5 BD+32 2132 Ursae Majoris, 53 0423 098230 1 055203 Alula Australis WISE objects