23 Librae

23 Librae (23 Lib) is a star in the zodiac constellation Libra, making it visible from most of the Earth's surface. With an apparent visual magnitude of 6.45,[2] it requires dark skies and good seeing conditions to see this star with the naked eye. It has a planetary system with two confirmed extrasolar planets.[3]

23 Librae
Observation data
Epoch J2000      Equinox J2000
Constellation Libra
Right ascension 15h 13m 28.6671s[1]
Declination −25° 18′ 33.6547″[1]
Apparent magnitude (V) 6.45[2]
Characteristics
Spectral type G5 V[3]
B−V color index +0.70[2]
Astrometry
Radial velocity (Rv)+4.7[4] km/s
Proper motion (μ) RA: −400.308±0.130[1] mas/yr
Dec.: −75.160±0.138[1] mas/yr
Parallax (π)38.1678 ± 0.0747[1] mas
Distance85.5 ± 0.2 ly
(26.20 ± 0.05 pc)
Details
Mass1.07+0.03
−0.08[3] M☉
Radius1.25±0.04[3] R☉
Surface gravity (log g)4.30[5] cgs
Temperature5585±50[3] K
Metallicity [Fe/H]0.25±0.02[3] dex
Rotational velocity (v sin i)2.17[3] km/s
Age8.4+1.6
−1.4 to 11.1+1.5
−3.7[3] Gyr
Other designations
CD−24° 11928, GJ 579.4, HD 134987, HIP 74500, HR 5657, SAO 183275.[6]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

Properties

Based upon parallax measurements, this star is located at a distance of 85 light-years (26 parsecs) from the Earth. The spectral properties of 23 Librae identify it as stellar class G5 V, with the luminosity class of 'V' indicating that this is a main sequence star that is generating energy through the thermonuclear fusion of hydrogen at its core. This energy is being radiated from the outer envelope at an effective temperature of about 5,585 K, giving it the yellow hue typical of G-type stars.[7] Estimates of the age of 23 Librae range from 8.4 to 11.1 billion years, making it much older than the Sun.[3]

23 Librae is slightly larger than the Sun, with an estimated 107% of the Sun's mass and 125% of the Sun's radius. The abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is higher than in the Sun. It appears to be rotating slowly, with the projected rotational velocity of 2.2 km∙s−1 giving a lower bound to the actual azimuthal velocity along the equator.[3]

Planetary system

In November 1999 an exoplanet 23 Librae b was announced orbiting 23 Librae,[8][9] and in 2009 an additional planet was detected.[3] Examination of the system in the infrared using the Spitzer Space Telescope did not reveal any excess emission, which might otherwise suggest the presence of a circumstellar debris disk of orbiting dust.[10] In the popular franchise Halo the star system is home to the planets Hesiod farther away from the star and Madrigal in the habitable zone.

The 23 Librae planetary system[3]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥ 1.59±0.02 MJ 0.81±0.02 258.19±0.07 0.233±0.002 — —
c ≥ 0.82±0.03 MJ 5.8±0.5 5000±400 0.12±0.02 — —

See also

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. 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
  3. Jones, Hugh R. A.; et al. (April 2010), "A long-period planet orbiting a nearby Sun-like star", Monthly Notices of the Royal Astronomical Society, 403 (4): 1703–1713, arXiv:0912.2716, Bibcode:2010MNRAS.403.1703J, doi:10.1111/j.1365-2966.2009.16232.x
  4. Holmberg, J.; Nordstrom, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191
  5. Sousa, S. G.; et al. (August 2007), "Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes", Astronomy and Astrophysics, 487 (1): 373–381, arXiv:0805.4826, Bibcode:2008A&A...487..373S, doi:10.1051/0004-6361:200809698
  6. "LTT 6066 -- High proper-motion Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-31
  7. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on February 22, 2012, retrieved 2012-01-16
  8. "Astronomers discover six new planets orbiting nearby stars" (Press release). Kamuela, Hawaii: W. M. Keck Observatory. November 1, 1999. Retrieved December 19, 2017.
  9. Vogt, Steven S.; et al. (2000), "Six New Planets from the Keck Precision Velocity Survey", The Astrophysical Journal, 536 (2): 902–914, arXiv:astro-ph/9911506, Bibcode:2000ApJ...536..902V, doi:10.1086/308981
  10. Dodson-Robinson, Sarah E.; et al. (January 2011). "A Spitzer Infrared Spectrograph Study of Debris Disks Around Planet-host Stars". The Astronomical Journal. 141 (1). arXiv:1010.3292. Bibcode:2011AJ....141...11D. doi:10.1088/0004-6256/141/1/11.

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