Beta Centauri is a triple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

in the southern

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 Centaurus. It is officially called Hadar (). The

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. ...

of Beta Centauri is Latinised from β Centauri, and abbreviated Beta Cen or β Cen. The system's combined apparent visual magnitude of 0.61 makes it the second-brightest object in Centaurus and one of the

brightest stars This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a ''V''-band filter in the UBV photometric system. Stars ...

in the night sky. According to

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 from the astrometric

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

satellite, the distance to this system is about .

Nomenclature

''β Centauri'' (Latinised to ''Beta Centauri'') is the star system's

. It bore the traditional names ''Hadar'' and ''Agena''. ''Hadar'' comes from the Arabic حضار (the root's meaning is "to be present" or "on the ground" or "settled, civilized area"), while the name ''Agena'' is thought to be derived from the Latin ''genua'', meaning "knees", from the star's position on the left knee of the

centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...

depicted in the constellation Centaurus. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name ''Hadar'' for the star β Centauri Aa on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. The Chinese name for the star is 马腹一 (

Mandarin Mandarin or The Mandarin may refer to: Language * Mandarin Chinese, branch of Chinese originally spoken in northern parts of the country ** Standard Chinese or Modern Standard Mandarin, the official language of China ** Taiwanese Mandarin, Stand ...

: mǎ fù yī, "the First Star of the Horse's Abdomen"). The

Boorong The Wergaia or Werrigia people are an Aboriginal Australian group in the Mallee and Wimmera regions of north-Western Victoria, made up of a number of clans. The people were also known as the Maligundidj (in the Wotjobaluk language) which means ...

people indigenous to what is now northwestern Victoria, Australia named it ''Bermbermgle'' (together with α Centauri), two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" ( Coalsack Nebula). The Wotjobaluk people name the two brothers ''Bram-bram-bult''.

Visibility

Beta Centauri is one of the

in the sky at magnitude 0.61. Its brightness varies by a few hundredths of a magnitude, too small to be noticeable to the naked eye. Because of its spectral type and the detection of pulsations, the Aa component has been classified as a β Cephei variable. Beta Centauri is well known in the Southern Hemisphere as the inner of the two "Pointers" to the constellation Crux, popularly known as the Southern Cross. A line made from the other pointer,

Alpha Centauri Alpha Centauri ( Latinized from α Centauri and often abbreviated Alpha Cen or α Cen) is a triple star system in the constellation of Centaurus. It consists of 3 stars: Alpha Centauri A (officially Rigil Kentaurus), Alpha Centaur ...

, through Beta Centauri leads to within a few degrees of Gacrux, the star at the north end of the cross. Using Gacrux, a navigator can draw a line with Acrux at the south end to effectively determine south.

Stellar system

The Beta Centauri system is made up of three

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s: Beta Centauri Aa, Beta Centauri Ab, and Beta Centauri B. All the spectral lines detected are consistent with a B1-type star, with only the line profiles varying, so it is thought that all three stars have the same spectral type. In 1935,

Joan Voûte Joan George Erardus Gijsbertus Voûte (7 June 1879 – 20 August 1963) was a Dutch astronomer. He was born in Madioen, Java to a Huguenot family. He studied civil engineering at Delft, but while a student he gained an interest in astronomy&mdash ...

identified Beta Centauri B, giving it the identifier VOU 31. The companion is separated from the primary by 1.3

seconds of arc 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 n ...

, and has remained so since the discovery, although the position angle has changed six degrees since. Beta Centauri B is a B1 dwarf with an apparent magnitude of 4. In 1967, Beta Centauri's observed variation in

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

suggested that Beta Centauri A 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 ...

. This was confirmed in 1999. It consists of a pair of stars, β Centauri Aa and β Centauri Ab, of similar mass that orbit each other over a period of 357 days with a large eccentricity of about 0.8245. The pair were calculated to be separated by a mean distance of roughly 4 astronomical units (based on a distance to the system of 161 parsecs) in 2005. Both Aa and Ab apparently have 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 B1 III, with the luminosity class of III indicating giant stars that are evolving away from the

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 ...

. Component Aa rotates much more rapidly than Ab, causing its spectral lines to be broader, and so the two components can be distinguished in the spectrum. Component Ab, the slow-rotating star, has a strong magnetic field although no detected abundance peculiarities in its spectrum. Multiple pulsations modes have been detected in component Aa, some of which correspond to brightness variations, so this star is considered to be variable. The detected pulsation modes correspond to those for both β Cephei variables and

slowly pulsating B star A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 ...

s. Similar pulsations have not been detected in component Ab, but it is possible that it is also a variable star. Aa is 12.02 ± 0.13 times as massive as the Sun, while Ab is 10.58 ± 0.18 times as massive.

References

{{DEFAULTSORT:Beta Centauri Centauri, Beta Beta Cephei variables B-type giants Centaurus (constellation) 122451 068702 Spectroscopic binaries Triple star systems Hadar

5267 5 (five) is a number, numeral and digit. It is the natural number, and cardinal number, following 4 and preceding 6, and is a prime number. It has attained significance throughout history in part because typical humans have five digits on eac ...

Durchmusterung objects