Beta Librae

Beta Librae (β Librae, abbreviated Beta Lib, β Lib), formally named Zubeneschamali /zuːˌbɛnɛʃəˈmeɪli/,[10][11] is (despite its 'beta' designation) the brightest star in the zodiac constellation of Libra. From parallax measurements, its distance can be estimated as 185 light-years (57 parsecs) from the Sun.[1]

Beta Librae
Diagram showing star positions and boundaries of the Libra constellation and its surroundings
The position of β Librae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Libra
Right ascension 15h 17m 00.41382s[1]
Declination −09° 22′ 58.4919″[1]
Apparent magnitude (V) 2.61[2]
Characteristics
Spectral type B8 V[3]
U−B color index −0.359[4]
B−V color index −0.106[4]
Variable type Suspected
Astrometry
Radial velocity (Rv)−35.2[2] km/s
Proper motion (μ) RA: −98.10[1] mas/yr
Dec.: −19.65[1] mas/yr
Parallax (π)17.62 ± 0.16 mas[1]
Distance185 ± 2 ly
(56.8 ± 0.5 pc)
Absolute magnitude (MV)−1.16[5]
Details
Mass3.5+0.3
−0.2[3] M☉
Radius4.9[6] R☉
Luminosity130 L☉
Temperature12300[7] K
Metallicity [Fe/H]0.33[3] dex
Rotational velocity (v sin i)250[8] km/s
Age80+50
−40[3] Myr
Other designations
Zubeneschamali, Kiffa Australis, Lanx Borealis, β Lib, 27 Librae, BD-08° 3935, FK5 564, HD 135742, HIP 74785, HR 5685, NSV 7009, SAO 140430[9]
Database references
SIMBADdata

The apparent visual magnitude of this star is 2.6.[2] According to Eratosthenes, Beta Librae was observed to be brighter than Antares. Ptolemy, 350 years later, said it was as bright as Antares. The discrepancy may be due to Antares becoming brighter, but this is not known for certain. It could simply be caused by Beta Librae being a variable star, showing a present-day variability of 0.03 of a magnitude.[12]

Name

β Librae (Latinised to Beta Librae) is the star's Bayer designation.

It bore the traditional name Zubeneschamali /ˌzuːbənˌɛʃəˈmeɪli/ (less common renderings, or corruptions, are Zuben Eschamali, Zuben el Chamali, Zubenesch, Zubenelg), derived from the Arabic الزُّبَانَى الشَمَالِي (al-zubānā al-šamāliyy) meaning "the northern claw". This name originated in a time when Libra was viewed as representing the "claws of the scorpion".[12] There was also Kiffa Borealis, from the Arabic al-kiffah aš-šamāliyy "the northern pan (of the scales)" and the Latin equivalent Lanx Borealis.[13] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Zubeneschamali for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[11]

In Chinese, 氐宿 (Dī Xiù), meaning Root, refers to an asterism consisting of β Librae, α2 Librae, ι Librae and γ Librae.[15] Consequently, the Chinese name for β Librae itself is 氐宿四 (Dī Xiù sì), "the Fourth Star of Root".[16]

Properties

Based upon the features of its spectrum, Beta Librae has a stellar classification of B8 V,[3] making it a B-type main-sequence star. It is about 130 times more luminous than the Sun and has a surface temperature of 12,300 K,[7] double that of the Sun. This high temperature produces light with a simple spectrum, making it ideal for examining the interstellar gas and dust between Earth and the star. Like many stars of its kind, it is spinning rapidly, over 100 times faster than the Sun with a projected rotational velocity of 250 km·s−1.[8] The measured angular diameter of the primary star is 0.801 mas.[7] At the estimated distance of this system, this yields a physical size of about 4.9 times the radius of the Sun.[6]

This type of massive, hydrogen-fusing star often appears blue-white, and is usually stated to be white or bluish by modern observers, but earlier observers often described Beta Librae as the only greenish star visible to the naked eye.[17] There seems to be no generally accepted explanation for why some observers see it as green.[18] The small periodic variations in the magnitude of Beta Librae suggest the presence of a companion star which is not directly observable from Earth.[19] However, it is categorized as a single star.[20]

See also

References
  1. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  3. Janson, Markus; et al. (August 2011), "High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood", The Astrophysical Journal, 736 (2): 89, arXiv:1105.2577, Bibcode:2011ApJ...736...89J, doi:10.1088/0004-637X/736/2/89, S2CID 119217803
  4. Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement, 15: 459, Bibcode:1968ApJS...15..459G, doi:10.1086/190168
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  6. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3 ed.), Birkhäuser, ISBN 3540296921. The radius (R*) is given by:
  7. Zorec, J.; et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics, 501 (1): 297–320, arXiv:0903.5134, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147, S2CID 14969137
  8. Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  9. "bet Lib". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-01-22.
  10. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  11. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  12. AAS (2006), "LIBRA – A Balanced View (page 7 of PDF)" (PDF), Auckland Astronomical Society, archived from the original (PDF) on 2012-02-12, retrieved 2009-01-25
  13. La Hire, Philippe (1727), Tabulae Astronomicae, Parisiis : Apud Montalant, typographum & bibliopolam ..., see star table, page 13.
  14. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  16. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. Kaler, James B. (2006), "Zubeneschamali", Stars, University of Illinois, archived from the original on 2006-07-14, retrieved 2006-07-03
  18. Burnham, Robert, Jr. (1978), Burnham's Celestial Handbook, vol. 2, New York: Dover Publications, p. 1105, ISBN 0-486-23568-8.{{citation}}: CS1 maint: multiple names: authors list (link)
  19. Mark Fisher (1999–2006), "Zuben Elschemali", The Electronic Sky, retrieved 2009-01-25
  20. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
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