Tau Librae

Tau Librae, Latinized from τ Librae, is the Bayer designation for a binary star system at the southern edge of the zodiac constellation of Libra. It can be seen with the naked eye, having an apparent visual magnitude of 3.68.[2] The distance to this system is around 367 light years, as determined from an annual parallax shift of 8.89 mas.[1]

Tau Librae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Libra
Right ascension  15h 38m 39.36950s[1]
Declination −29° 46′ 39.8956″[1]
Apparent magnitude (V) 3.68[2]
Characteristics
Spectral type B2.5 V[3]
U−B color index −0.717[2]
B−V color index −0.179[2]
Astrometry
Radial velocity (Rv)+33.3±2.3[4] km/s
Proper motion (μ) RA: −22.08[1] mas/yr
Dec.: −24.46[1] mas/yr
Parallax (π)8.89 ± 0.20[1] mas
Distance367 ± 8 ly
(112 ± 3 pc)
Absolute magnitude (MV)−1.59[5]
Orbit[6]
Period (P)3.2907 d
Eccentricity (e)0.28
Longitude of the node (Ω)114°
Periastron epoch (T)2439272.312 JD
Semi-amplitude (K1)
(primary)		75 km/s
Semi-amplitude (K2)
(secondary)		167 km/s
Details
τ Lib A
Mass7.25±0.49[7] M☉
Radius3.2[8] R☉
Luminosity (bolometric)2,705[7] L☉
Surface gravity (log g)4.33[9] cgs
Temperature17,990[9] K
Metallicity [Fe/H]+0.17[9] dex
Rotational velocity (v sin i)134[4] km/s
Age31.5±5.6[10] Myr
Other designations
τ Lib, 40 Lib, CD−29° 11837, HD 139365, HIP 76600, HR 5812, SAO 183649.[11]
Database references
SIMBADdata

Judging by its motion through space and physical properties, this system is a member of the Upper Centaurus Lupus group of the Scorpius-Centaurus Association.[4] It is double-lined[12] spectroscopic binary with an orbital period of just 3.3 days and an eccentricity of 0.28.[6] The primary, component A, is a B-type main sequence star with a stellar classification of B2.5 V.[3] It is estimated to hold more than seven[7] times the mass of the Sun and have over three[8] times the Sun's radius. It is only 31.5[10] million years old and is spinning relatively rapidly with a projected rotational velocity of 134 km/s.[4]

The system is emitting an infrared excess, suggesting the presence of a circumstellar disk of material.[9]

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. 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.
  3. Hiltner, W. A.; Garrison, R. F.; Schild, R. E. (July 1969), "MK Spectral Types for Bright Southern OB Stars", Astrophysical Journal, 157: 313–326, Bibcode:1969ApJ...157..313H, doi:10.1086/150069.
  4. Jilinski, E.; et al. (March 2006), "Radial velocity measurements of B stars in the Scorpius-Centaurus association", Astronomy and Astrophysics, 448 (3): 1001–1006, arXiv:astro-ph/0601643, Bibcode:2006A&A...448.1001J, doi:10.1051/0004-6361:20041614.
  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. Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  7. Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  8. 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.
  9. Saffe, C.; Gómez, M.; Pintado, O.; González, E. (October 2008), "Spectroscopic metallicities of Vega-like stars", Astronomy and Astrophysics, 490 (1): 297–305, arXiv:0805.3936, Bibcode:2008A&A...490..297S, doi:10.1051/0004-6361:200810260.
  10. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  11. "tau Lib". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-01-30.
  12. Strom, Stephen E.; et al. (February 2005), "B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?", The Astronomical Journal, 129 (2): 809–828, arXiv:astro-ph/0410337, Bibcode:2005AJ....129..809S, doi:10.1086/426748.
  • Kaler, James B. (May 17, 2013), "Tau Librae", Stars, University of Illinois, retrieved 2017-02-02.
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