Gamma Librae

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Gamma Librae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Libra
Right ascension  15h 35m 31.57881s[1]
Declination −14° 47′ 22.3278″[1]
Apparent magnitude (V) +3.91[2]
Spectral type G8.5 III[3]
Radial velocity (Rv)−26.71[4] km/s
Proper motion (μ) RA: +65.34[1] mas/yr
Dec.: +7.45[1] mas/yr
Parallax (π)19.99 ± 0.20[1] mas
Distance163 ± 2 ly
(50.0 ± 0.5 pc)
Absolute magnitude (MV)−1.59[5]
γ Lib A
Mass1.15 M
Radius11.14 R
Luminosity72 L
Surface gravity (log g)2.55 cgs
Temperature4,786 K
Metallicity [Fe/H]−0.30 dex
Rotational velocity (v sin i)1.60 km/s
Age4.31 Gyr
Other designations
Zubenelhakrabi, γ Lib, 38 Lib, BD−14° 4237, FK5 577, HD 138905, HIP 76333, HR 5787, SAO 159370, WDS J15355-1447A[6]
Database references

Gamma Librae (γ Librae, abbreviated Gam Lib, γ Lib) is a suspected[7] binary star system in the constellation of Libra. It is visible to the naked eye, having an apparent visual magnitude of +3.91.[2] Based upon an annual parallax shift of 19.99 mas as seen from Earth, it lies 163 light years from the Sun.

The primary component (designated Gamma Librae A) is named Zubenelhakrabi.[8]


γ Librae (Latinised to Gamma Librae) is the system's Bayer designation. The designations of the two components as Gamma Librae A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[9]

Gamma Librae bore the traditional name Zuben (el) Hakrabi (also rendered as Zuben-el-Akrab and corrupted as Zuben Hakraki). The name is a modification of the Arabic زبانى العقرب Zuban al-ʿAqrab "the claws of the scorpion", a name that dates to before Libra was a distinct constellation from Scorpius.[citation needed] In 2016, the IAU organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[11] It approved the name Zubenelhakrabi for the component Gamma Librae A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[8]

In Chinese, 氐宿 (Dī Xiù), meaning Root, refers to an asterism consisting of Gamma Librae, Alpha² Librae, Iota Librae and Beta Librae.[12] Consequently, the Chinese name for Gamma Librae itself is 氐宿三 (Dī Xiù sān), "the Third Star of Root".[13]


Because the star lies near the ecliptic it is subject to occultations by the Moon, allowing the angular size to be measured.[14] As of 1940, the pair had an angular separation of 0.10 arc seconds along a position angle of 191°.[15]

The yellow-hued primary, component Aa, is an evolved G-type giant star with a stellar classification of G8.5 III[3] and an estimated age of 4.3 billion years. It has 1.15 times the mass of the Sun and has expanded to 11.14 times the Sun's radius. The star is radiating around 72 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,786 K.[4] There is a magnitude 11.2 visual companion, component B, at an angular separation of 42.5 arc seconds along a position angle of 157°, as of 2013.[15]

At its distance, the visual magnitude is diminished by an extinction of 0.11 due to interstellar dust.[2] The system is moving closer to the Sun with a radial velocity of −26.71 km/s.[4]

Planetary system[edit]

On the 11th of April 2018 the discovery of two gas giant planets orbiting Gamma Librae was announced. [16]

The Gamma Librae planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 1.24 415.2 0.21 ± 0.10
c 2.17 964.6 ± 3.1 0.057


  1. ^ a b c d e van Leeuwen, F. (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.
  2. ^ a b c Takeda, Yoichi; et al. (August 2008), "Stellar Parameters and Elemental Abundances of Late-G Giants", Publications of the Astronomical Society of Japan, 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781.
  3. ^ a b Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. ^ a b c d Jofré, E.; et al. (February 2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: 46, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, A50.
  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.
  6. ^ "HD 138905 -- Double or multiple star". SIMBAD Astronomical Database. Retrieved 2007-01-22.
  7. ^ Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  8. ^ a b "Naming Stars". Retrieved 16 December 2017.
  9. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  10. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  12. ^ (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.
  13. ^ (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.
  14. ^ White, Nathaniel M.; Feierman, Barry H. (September 1987), "A Catalog of Stellar Angular Diameters Measured by Lunar Occultation", Astronomical Journal, 94: 751, Bibcode:1987AJ.....94..751W, doi:10.1086/114513.
  15. ^ a b Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
  16. ^ "Planets around the evolved stars 24 Booties and γ Libra: A 30d-period planet and a double giant-planet system in possible 7:3 MMR". Takuya Takarada, Bun'ei Sato, Masashi Omiya, Hiroki Harakawa, Makiko Nagasawa, Hideyuki Izumiura, Eiji Kambe, Yoichi Takeda, Michitoshi Yoshida, Yoichi Itoh, Hiroyasu Ando, Eiichiro Kokubo, Shigeru Ida (April 11, 2018).