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Epsilon Librae (ε Lib) is the Bayer designation for a binary star system in the zodiac constellation Libra. With an apparent visual magnitude of 4.922, it is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 32.02 mas, it is located about 102 light years away from the Sun.

This is a single-lined spectroscopic binary star system. The pair orbit each other with a period of 226.9 days and an eccentricity of 0.66. The semimajor axis of their orbit is estimated to be 0.85 AU, or 85% of the distance from the Earth to the Sun. The primary, component A, has been catalogued with stellar classifications of F3 V and F5 IV, suggesting that it is an F-type star that either belongs to the main sequence or has evolved into a subgiant as the hydrogen at its core nears exhaustion.

The primary has an estimated 1.17 times the mass of the Sun and 1.5 times the Sun's radius. It is around 1.5 billion years old and is spinning with a projected rotational velocity of 10 km/s. The star radiates 9.3 times the solar luminosity from its outer atmosphere at an effective temperature of 6,552 K. The secondary, component B, has 41% of the Sun's mass.

References

1. ^ 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, S2CID 18759600.
2. ^ Celis, L. (October 1975), "Photoelectric photometry of late-type variable stars", Astronomy and Astrophysics Supplement Series, 22: 9–17, Bibcode:1975A&AS...22....9C.
3. ^ Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Ann Arbor, Michigan: Department of Astronomy, University of Michigan, Bibcode:1999MSS...C05....0H.
4. ^ Malaroda, S. (August 1975), "Study of the F-type stars. I. MK spectral types", Astronomical Journal, 80: 637–641, Bibcode:1975AJ.....80..637M, doi:10.1086/111786.
5. ^ Takeda, Yoichi; et al. (February 2005), "High-Dispersion Spectra Collection of Nearby F--K Stars at Okayama Astrophysical Observatory: A Basis for Spectroscopic Abundance Standards", Publications of the Astronomical Society of Japan, 57 (1): 13–25, Bibcode:2005PASJ...57...13T, doi:10.1093/pasj/57.1.13.
6. ^ Katoh, Noriyuki; et al. (February 2013), "Determination of Orbital Elements of Spectroscopic Binaries Using High-dispersion Spectroscopy", The Astronomical Journal, 145 (2): 12, Bibcode:2013AJ....145...41K, doi:10.1088/0004-6256/145/2/41, 41.
7. Jancart, S. (2005), "Astrometric orbits of S_B stars", Astronomy and Astrophysics, 442 (1): 365–380, arXiv:astro-ph/0507695, Bibcode:2005A&A...442..365J, doi:10.1051/0004-6361:20053003, S2CID 15123997.
8. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; et al. (2004), "S_B: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
9. Pasinetti-Fracassini, L. E.; et al. (February 2001), "Catalog of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics, 367 (3rd ed.): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
10. ^ Takeda, Yoichi (April 2007), "Fundamental Parameters and Elemental Abundances of 160 F-G-K Stars Based on OAO Spectrum Database", Publications of the Astronomical Society of Japan, 59 (2): 335–356, Bibcode:2007PASJ...59..335T, doi:10.1093/pasj/59.2.335.
11. "eps Lib -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-01-30.

v t e Constellation of Libra
List of stars in Libra Libra in Chinese astronomy
Stars	Bayer α α (Zubenelgenubi) β (Zubeneschamali) γ (Zubenelhakrabi) δ (Zuben Elakribi) ε ζ ζ ζ ζ η θ ι ι κ λ μ ν ξ ξ ο σ (Brachium) τ υ Flamsteed 2 3 4 5 10 11 12 16 17 18 22 23 26 28 30 36 37 41 42 47 48 49 50 30 Ser Variable HO KU KX HR 5455 HD 133112 133131 134439 134440 139139 140283 141569 141937 Other 2M1510 2MASS 1507−1627 Gliese 555 HE 1523-0901 WASP-57 WISE 1541−2250
Exoplanets 23 Librae b c γ Librae b c Gliese 581b c e WASP-189b
Star clusters NGC 5897
Galaxies	NGC 5605 5728 5792 5793 5861 5885 5890 5898 5917 Other AP IC 1059 IRAS 14348-1447 PKS 1510-089
Category

• F-type main-sequence stars
• Spectroscopic binaries
• Libra (constellation)
• Bayer objects
• Durchmusterung objects
• Flamsteed objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Bright Star Catalogue objects