Delta Librae

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δ Librae
Observation data
Epoch J2000      Equinox J2000
Constellation Libra
Right ascension  15h 00m 58.35013s[1]
Declination −08° 31′ 08.2063″[1]
Apparent magnitude (V) 4.93[2]
Spectral type B9.5V[3]
U−B color index –0.10[4]
B−V color index +0.00[4]
Variable type Eclipsing binary of Algol type (EA/SD)[5]
Radial velocity (Rv)−38.7±2[6] km/s
Proper motion (μ) RA: -63.46[1] mas/yr
Dec.: -4.76[1] mas/yr
Parallax (π)11.11 ± 0.60[1] mas
Distance290 ± 20 ly
(90 ± 5 pc)
Absolute magnitude (MV)+0.15[7]
Period (P)2.3274 d
Eccentricity (e)0.07
Semi-amplitude (K1)
76.6 km/s
Semi-amplitude (K2)
218.7 km/s
δ Lib A
Mass4.9±0.2[8] M
Radius3.94[9] R
Luminosity86[7] L
Temperature8800[9] K
Age0.5[9] Gyr
δ Lib B
Mass1.7±0.2[8] M
Other designations
δ Lib, Zuben Elakribi, 19 Librae, BD–07° 3938, HD 132742, HIP 73473, HR 5586, SAO 140270
Database references

Delta Librae, Latinized from δ Librae, is a variable star in the constellation Libra. It has the traditional name Zuben Elakribi, a variant of the traditional name of Gamma Librae.[10] With μ Vir it forms one of the Akkadian lunar mansions Mulu-izi[11] (meaning "Man-of-fire"[12]).

δ Lib is approximately 300 light years from the Earth and the primary, component A, belongs to the spectral class B9.5V, indicating it is a B-type main-sequence star. It is visible to the naked eye with an apparent visual magnitude of 4.93[2] and is moving closer to the Sun with a radial velocity of −39 km/s.[6] This is an Algol-like eclipsing binary star system, with a period of 2.3274 days and an eccentricity of 0.07.[8] Its apparent magnitude varies from 4.91m to 5.9m.[13] The secondary is filling its roche lobe and there is evidence of large-scale mass transfer in the past, with the star being more evolved than the primary.[8]

Along with λ Tau, it was one of the first stars on which rotational line broadening[14] was observed, by Frank Schlesinger in 1911.


  1. ^ a b c d e van Leeuwen, F.; et al. (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 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. ^ Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
  4. ^ a b Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4. Bibcode:1966CoLPL...4...99J.
  5. ^ "Del Lib". The International Variable Star Index. AAVSO – American Association of Variable Star Observers. Retrieved 27 September 2017.
  6. ^ a b Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Bibcode:1953GCRV..C......0W.
  7. ^ a b 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.
  8. ^ a b c d e Tomkin, J. (April 1978), "Secondaries of eclipsing binaries. I. Detection of the secondary of Delta Librae", Astrophysical Journal, 221: 608–615, Bibcode:1978ApJ...221..608T, doi:10.1086/156064.
  9. ^ a b c Rhee, Joseph H.; Song, Inseok; Zuckerman, B.; McElwain, Michael (2007). "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs". The Astrophysical Journal. 660 (2): 1556–1571. arXiv:astro-ph/0609555. Bibcode:2007ApJ...660.1556R. doi:10.1086/509912.
  10. ^ Bečvář, A., Atlas Coeli II Atlas Coeli II- Catalog, Ceskoslovenské Akademie Ved, Praha,1959.
  11. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. pp. 277, 473.
  12. ^ Brown Jr., R., (1891). "Remarks on the Euphratean Astronomical Names of the Signs of the Zodiac", Proceedings of the Society of Biblical Archaeology, vo. 13, p. 194.
  13. ^ Samus, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, retrieved 2018-01-07.
  14. ^ Schlesinger, F. (1909), "Rotation of Stars about their Axes", Monthly Notices of the Royal Astronomical Society, 71: 719, Bibcode:1911MNRAS..71..719S, doi:10.1093/mnras/71.9.719.