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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 0.61, 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"〔Hans Wehr, ''A dictionary of modern written Arabic'', 1961〕), 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'').〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 29 日 )〕 ==Properties== The Beta Centauri system has three components: Beta Centauri A1, A2 and 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. According to parallax measurements from the astrometric Hipparcos satellite,〔〔 the distance to this system is about .〔 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 the primary at 0.6 light years, or 100k AUs, with a period of roughly 1500 years. Beta Centauri B is a B1 dwarf with an apparent magnitude of 4. 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 0.825. The pair are separated by a mean distance of roughly 4 astronomical units.〔 Both A1 and A2 apparently have a stellar classification of B1 III,〔 with the luminosity class of III indicating giant stars that are evolving away from the main sequence. They are both Beta Cephei variable stars with multiple pulsation periods of just a few hours. The full range of variability has not been identified, but is no more than a few hundredths of a magnitude.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Beta Centauri」の詳細全文を読む スポンサード リンク
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