Epoch J2000 Equinox J2000
|Right ascension||14h 03m 49.40535s|
|Declination||–60° 22′ 22.9266″|
|Apparent magnitude (V)||0.60|
|Radial velocity (Rv)||+5.9 km/s|
|Proper motion (μ)||RA: –33.27 mas/yr
Dec.: –23.16 mas/yr
|Parallax (π)||9.35 ± 0.50 mas|
|Distance||350 ± 20 ly
(107 ± 6 pc)
|Spectral type||B1 III|
|U−B color index||–0.98|
|B−V color index||–0.22|
|Variable type||β Cep|
|Mass||10.7 ± 0.1 / 10.3 ± 0.1 M☉|
|Surface gravity (log g)||3.5 ± 0.4 cgs|
|Temperature||25,000 ± 2,000 K|
|Age||(14.1 ± 0.6) × 106 years|
Beta Centauri (β Cen, β Centauri) is a trinary star system in the southern constellation of Centaurus. The system's combined apparent visual magnitude of 0.60, makes it the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky. It has the traditional names Hadar and Agena. The name 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 may ultimately be derived from the Latin gena 'knees'. The Chinese name for the star is 马腹一 (Mandarin: mǎ fù yī, the First Star of the Horse's Abdomen).
The Beta Centauri system has three components: Beta Centauri A1, A2 and B.
According to parallax measurements from the astrometric Hipparcos satellite, the distance to this system is about 350 light-years (110 parsecs). The spectrum matches a star with a stellar classification of B1 III, with the luminosity class of III indicating Beta Centauri A1 and A2 are both giant stars that have exhausted the hydrogen at its core and evolved away from the main sequence. They are both Beta Cephei variable stars with a pulsation period of 0.157 days.
In 1967, Beta Centauri's observed periodic variation in radial velocity suggested that Beta Centauri A is a double-lined spectroscopic binary. This was confirmed in 1999. The primary consists of a pair of stars, (A1 and A2) with nearly identical mass that orbit each other over a period of 357 days with a large eccentricity of about 0.81. The pair are separated by a mean distance of roughly 4 astronomical units.
In 1935, Joan Voûte identified Beta Centauri B, giving it the identifier VOU 31. The companion is separated from the primary by 1.3 seconds of arc, and has remained so since the discovery, although the position angle has changed six degrees since. Beta Centauri B orbits A1 and A2 at .6 light years, or 100k AUs, with a period of roughly 1500 years. Beta Centauri B is a B1 Dwarf with an apparent magnitude of 3.7, and an absolute magnitude of -1.5, similar to that of Achernar.
Beta Centauri is well known in the Southern Hemisphere as the inner of the two "Pointers" to the Southern Cross. A line made from the other pointer, Alpha Centauri, through Beta Centauri leads to within a few degrees of Gacrux, the star at the top of the cross. Using Gacrux, a navigator can draw a line with Acrux to effectively determine south.
The indigenous Boorong people of northwestern Victoria named it as Bermbermgle (together with α Cen), two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" (Coalsack Nebula). The two brothers in Wotjobaluk people is Bram-bram-bult.
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