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Beta Centauri

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Beta Centauri

β Centauri

Location of β Centauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 14h 03m 49.40535s[1]
Declination –60° 22′ 22.9266″[1]
Apparent magnitude (V) 0.61[2]
Radial velocity (Rv) +5.9[3] km/s
Proper motion (μ) RA: –33.27[1] mas/yr
Dec.: –23.16[1] mas/yr
Parallax (π) 8.32 ± 0.50[1] mas
Distance 390 ± 20 ly
(120 ± 7 pc)
Absolute magnitude (MV) −4.53[4]
U−B color index –0.98[2]
B−V color index –0.23[2]
β Cen A1
Spectral type B1 III[5]
Variable type β Cep[6]
β Cen A2
Spectral type B1 III[5]
Variable type β Cep[6]
β Cen B
Spectral type B1V?[5]
Primary β Cen A1
Companion β Cen A2
Period (P) 356.94 days
Semi-major axis (a) 0.0253"
Eccentricity (e) 0.825
Inclination (i) 67.4°
Periastron epoch (T) 2451600.08
Argument of periastron (ω)
Semi-amplitude (K1)
57.4 km/s
Semi-amplitude (K2)
72.3 km/s
Primary β Cen A
Companion β Cen B
Period (P) 288.267 yr
Semi-major axis (a) 0.870"
Luminosity 41,700[8] L
Age 14.1 ± 0.6[5] Myr
β Cen A1
Mass 10.7 ± 0.1[5] M
Surface gravity (log g) 3.5 ± 0.4[5] cgs
Temperature 25,000 ± 2,000[5] K
β Cen A2
Mass 10.3 ± 0.1[5] M
Surface gravity (log g) 3.5 ± 0.4[5] cgs
Temperature 25,000 ± 2,000[5] K
β Cen B
Mass 4.61[7] M
Other designations
Agena, Hadar,[9] HR 5267, HD 122451, CD−59°5365, LHS 51, SAO 252582, FK5 518 , HIP 68702, GC 18971, CCDM J14038-6022[10]
Database references

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"[11]), 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).[12]


  • Properties 1
  • Cultural significance 2
  • References 3
  • External links 4


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,[13][14] the distance to this system is about 400 light-years (120 parsecs).[1]

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.[8]

Both A1 and A2 apparently have a stellar classification of B1 III,[8] 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.[8][15]

Cultural significance

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.[16]

The indigenous Boorong people of northwestern Victoria named it as Bermbermgle (together with α Cen),[17] two brothers who were noted for their courage and destructiveness, and who spear and kill Tchingal, "The Emu" (Coalsack Nebula).[18] The two brothers in Wotjobaluk people is Bram-bram-bult.[17]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664,  
  2. ^ a b c Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven, Conn.: Yale University Observatory, 5th rev.ed.  
  3. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, retrieved 2009-09-10 
  4. ^ Davis, J.; Mendez, A.; Seneta, E. B.; Tango, W. J.; Booth, A. J.; O'Byrne, J. W.; Thorvaldson, E. D.; Ausseloos, M.; Aerts, C.; Uytterhoeven, K. (2005). "Orbital parameters, masses and distance to β Centauri determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy". Monthly Notices of the Royal Astronomical Society 356 (4): 1362.  
  5. ^ a b c d e f g h i j k Ausseloos, M.; et al. (August 2006), "High-precision elements of double-lined spectroscopic binaries from combined interferometry and spectroscopy. Application to the β Cephei star β Centauri", Astronomy and Astrophysics 455 (1): 259–269,  
  6. ^ a b Ausseloos, M.; Aerts, C.; Uytterhoeven, K.; Schrijvers, C.; Waelkens, C.; Cuypers, J. (2002). "Beta Centauri: An eccentric binary with two beta Cep-type components". Astronomy and Astrophysics 384: 209.  
  7. ^ a b Tokovinin, A. A. (1999). "VizieR Online Data Catalog: Multiple star catalogue (MSC) (Tokovinin 1997-1999)". VizieR On-line Data Catalog: J/A+AS/124/75. Originally published in: 1997A&AS..124...75T 412: 40075.  
  8. ^ a b c d Raassen, A. J. J.; et al. (July 2006), "XMM-Newton observations of β Centauri (B1 III): The temperature structure in the hot plasma and the photosphere-wind connection", Astronomy and Astrophysics 437 (2): 599–609,  
  9. ^  
  10. ^ "V* bet Cen -- Variable Star of beta Cep type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-19 
  11. ^ Hans Wehr, A dictionary of modern written Arabic, 1961
  12. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 29 日
  13. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics 323: L49–L52,  
  14. ^ Perryman, Michael (2010), The Making of History's Greatest Star Map, Heidelberg: Springer-Verlag,  
  15. ^ Sterken, Christiaan; Jerzykiewicz, Mikolaj (1993). "Beta Cephei stars from a photometric point of view". Space Science Reviews 62 (1-2): 95–171.  
  16. ^ Kyselka, Will; Lanterman, Ray E. (1976), North Star to Southern Cross, University of Hawaii Press, p. 59,  
  17. ^ a b Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae" (PDF). Journal of Astronomical History & Heritage 13 (3): 220–34. 
  18. ^ Stanbridge, WM (1857). "On the Astronomy and Mythology of the Aboriginies of Victoria" (PDF). Transactions Philosophical Institute Victoria 2: 137–140. 

External links

  • Kaler, James B., "HADAR (Beta Centauri)", Stars (University of Illinois), retrieved 2011-12-19 

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