Theta Librae

θ Librae, Latinised as Theta Librae, is a single[9] star in the southern zodiac constellation of Libra, near the constellation border with Scorpius. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.14.[2] The distance to this star is approximately 168 light years, as determined by parallax, and it is drifting further away with a radial velocity of 5 km/s.[5] The position of this star near the ecliptic means it is subject to lunar occultations.[10]

θ Librae
Location of θ Librae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Libra
Right ascension  15h 53m 49.53806s[1]
Declination –16° 43′ 45.4582″[1]
Apparent magnitude (V) 4.136[2]
Characteristics
Spectral type G9IIIb[3]
U−B color index +0.82[4]
B−V color index +1.01[4]
Astrometry
Radial velocity (Rv)4.56±0.25[5] km/s
Proper motion (μ) RA: +100.33[1] mas/yr
Dec.: +135.02[1] mas/yr
Parallax (π)19.36 ± 0.15[6] mas
Distance168 ± 1 ly
(51.7 ± 0.4 pc)
Absolute magnitude (MV)0.665[2]
Details
Mass1.47[7] M☉
Radius12.27[7] R☉
Luminosity68.1[7] L☉
Surface gravity (log g)2.44[7] cgs
Temperature4,739[7] K
Metallicity [Fe/H]–0.35[7] dex
Rotational velocity (v sin i)0.0[5] km/s
Age3.4[7] Gyr
Other designations
θ Lib, 46 Librae, BD−16°4174, HD 142198, HIP 77853, HR 5908, SAO 159563[8]
Database references
SIMBADdata

This object is an aging giant star with a stellar classification of G9IIIb.[3] Having exhausted the supply of hydrogen at its core, it has cooled and expanded; at present it has 12.3 times the girth of the Sun.[7] The star has an estimated mass about 47% greater than the Sun. It is radiating about 68 times the luminosity of the Sun from its photosphere at an effective temperature of about 4,739 K.[7] It is probably on the red giant branch, which indicates it is generating energy through hydrogen fusion in a shell outside an inert helium core.[7] However, there is a 41% chance that it is a red clump giant on the horizontal branch,[2] which would mean it was somewhat older and less massive.[7] It has sometimes been classified spectroscopically as a subgiant, but detailed study shows that it is too cool and luminous to be on the subgiant branch.[11]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Liu, Y. J.; et al. (2007). "The abundances of nearby red clump giants". Monthly Notices of the Royal Astronomical Society. 382 (2): 553–66. Bibcode:2007MNRAS.382..553L. doi:10.1111/j.1365-2966.2007.11852.x.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
  5. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  6. 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.
  7. Reffert, Sabine; Bergmann, Christoph; Quirrenbach, Andreas; Trifonov, Trifon; Künstler, Andreas (2015). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity". Astronomy and Astrophysics. 574: A116. arXiv:1412.4634. Bibcode:2015A&A...574A.116R. doi:10.1051/0004-6361/201322360.
  8. "tet Lib". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-06-19.
  9. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  10. Edwards, D. A.; et al. (April 1980). "Photoelectric observations of lunar occultations. XI". Astronomical Journal. 85: 478–489. Bibcode:1980AJ.....85..478E. doi:10.1086/112700.
  11. Thorén, P.; Edvardsson, B.; Gustafsson, B. (2004). "Subgiants as probes of galactic chemical evolution". Astronomy and Astrophysics. 425: 187–206. arXiv:astro-ph/0407260. Bibcode:2004A&A...425..187T. doi:10.1051/0004-6361:20040421.
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