Beta Librae

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[1] mas
Distance185 ± 2 ly
(56.8 ± 0.5 pc)
Details
Mass3.5+0.3
−0.2[3] M☉
Radius4.9[5] R☉
Luminosity130 L☉
Temperature12300[6] K
Metallicity [Fe/H]0.33[3] dex
Rotational velocity (v sin i)250[7] km/s
Age80+50
−40[3] Myr
Other designations
Zubeneschemali, Lanx Borealis, 27 Librae, BD-08 3935, FK5 564, HD 135742, HIP 74785, HR 5685, NSV 7009, SAO 140430.[8]

Beta Librae (β Librae, abbreviated Beta Lib, β Lib), also named Zubeneschamali,[9] 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]

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.[10]

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 ّالزُبَانَى الشَمَالِي (al-zubānā al-šamāliyy) meaning "The Northern Claw".[10] There was also Kiffa Borealis, from the Arabic al-kiffah aš-šamāliyy "the northern pan (of the scales)" and the Latin equivalent Lanx Borealis.[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] 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.[9]

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 12300 K,[6] 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.[7] The measured angular diameter of the primary star is 0.801 mas.[6] At the estimated distance of this system, this yields a physical size of about 4.9 times the radius of the Sun.[5] 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.[13] There seems to be no generally accepted explanation for why some observers see it as green.

The small periodic variations in the magnitude of Beta Librae suggest the presence of a companion star which is not directly observable from Earth.[14] However, it is categorized as a single star.[15]

See also

References

  1. 1 2 3 4 5 6 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 1 2 3 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. 1 2 3 4 5 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:1105.2577Freely accessible, Bibcode:2011ApJ...736...89J, doi:10.1088/0004-637X/736/2/89
  4. 1 2 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. 1 2 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3 ed.), Birkhäuser, ISBN 3540296921. The radius (R*) is given by:
  6. 1 2 3 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:0903.5134Freely accessible, Bibcode:2009A&A...501..297Z, doi:10.1051/0004-6361/200811147
  7. 1 2 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
  8. ↑ "HD 135742 -- Variable Star", SIMBAD Astronomical Object Database, retrieved 2007-01-22
  9. 1 2 "IAU Catalog of Star Names". Retrieved 28 July 2016.
  10. 1 2 AAS (2006), "LIBRA – A Balanced View (page 7 of PDF)" (PDF), Auckland Astronomical Society, retrieved 2009-01-25
  11. ↑ La Hire, Philippe (1727), Tabulae Astronomicae, see star table, page 13.
  12. ↑ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  13. ↑ Kaler, James B. (2006), "Zubeneschamali", Stars, University of Illinois, retrieved 2006-07-03
  14. ↑ Mark Fisher (1999–2006), "Zuben Elschemali", The Electronic Sky, retrieved 2009-01-25
  15. ↑ 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:0806.2878Freely accessible. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.

Coordinates: 15h 17m 00.41382s, −09° 22′ 58.4919″

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