Epsilon Librae

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,[2] it is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 32.02 mas,[1] it is located about 102 light years away from the Sun.

Epsilon Librae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Libra
Right ascension  15h 24m 11.89101s[1]
Declination −10° 19′ 20.1740″[1]
Apparent magnitude (V) 4.922[2]
Characteristics
Spectral type F3 V[3] or F5 IV[4]
U−B color index +0.080[2]
B−V color index +0.451[2]
Astrometry
Proper motion (μ) RA: −66.52[1] mas/yr
Dec.: −154.24[1] mas/yr
Parallax (π)32.02 ± 0.72[1] mas
Distance102 ± 2 ly
(31.2 ± 0.7 pc)
Absolute magnitude (MV)2.37[5]
Orbit[6]
Period (P)226.9437±0.0025 d
Semi-major axis (a)0.85192±0.00359 au
Eccentricity (e)0.6649±0.0014
Inclination (i)52.6±9.4[7]°
Periastron epoch (T)2453593.022 ± 0.041 HJD[8]
Argument of periastron (ω)
(secondary)		339.84±0.15°
Details
ε Lib A
Mass1.17±0.02[6] M☉
Radius1.5[9] R☉
Luminosity9.3[10] L☉
Surface gravity (log g)4.13[10] cgs
Temperature6,552±80[6] K
Metallicity [Fe/H]+0.09[10] dex
Rotational velocity (v sin i)10[5] km/s
Age1.5[10] Gyr
ε Lib B
Mass0.410±0.004[6] M☉
Other designations
ε Lib, 31 Lib, BD−09° 4138, HD 137052, HIP 75379, HR 5723, SAO 159234.[11]
Database references
SIMBADdata

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.[6] 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[3] and F5 IV,[4] 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[6] times the mass of the Sun and 1.5 times the Sun's radius. It is around 1.5[10] billion years old and is spinning with a projected rotational velocity of 10[5] km/s. The star radiates 9.3[10] times the solar luminosity from its outer atmosphere at an effective temperature of 6,552 K.[6] The secondary, component B, has 41% of the Sun's mass.[6]

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.
  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, Ann Arbor, Michigan: Department of Astronomy, University of Michigan, 5, 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 SB9 stars", Astronomy and Astrophysics, 442 (1): 365–380, arXiv:astro-ph/0507695, Bibcode:2005A&A...442..365J, doi:10.1051/0004-6361:20053003.
  8. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  9. Pasinetti-Fracassini, L. E.; et al. (February 2001), "Catalog of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  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.
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