Lambda Horologii

λ Horologii, Latinised as Lambda Horologii, is a star in the southern constellation of Horologium. It is a yellow-white hued star that is dimly visible to the naked eye with an apparent visual magnitude of +5.35.[2] Based upon parallax, this object is located 155 light years distance from the Sun. It is drifting further away with a radial velocity of +28 km/s.[1] Although Eggleton and Tokovinin (2008) list this as a single star,[8] according to Kunzli and North (1998) it may be a binary system with a long orbital period.[9]

Lambda Horologii
Observation data
Epoch J2000      Equinox J2000
Constellation Horologium
Right ascension  02h 24m 53.91034s[1]
Declination −60° 18′ 43.0170″[1]
Apparent magnitude (V) +5.35[2]
Characteristics
Spectral type F2III[3]
B−V color index +0.39[2]
Astrometry
Radial velocity (Rv)+28.34±0.41[1] km/s
Proper motion (μ) RA: −71.892[1] mas/yr
Dec.: −131.088[1] mas/yr
Parallax (π)21.0119 ± 0.1004[1] mas
Distance155.2 ± 0.7 ly
(47.6 ± 0.2 pc)
Absolute magnitude (MV)+1.91[4]
Details
Mass1.76[5] M☉
Radius2.74+0.11
−0.16[1] R☉
Luminosity13.3±0.1[1] L☉
Surface gravity (log g)3.66[6] cgs
Temperature6,848[5] K
Metallicity [Fe/H]−0.12[5] dex
Rotational velocity (v sin i)+140[3] km/s
Age1.4[5] Gyr
Other designations
λ Hor, CPD−60° 199, FK5 84, HD 15233, HIP 11258, HR 714, SAO 248555[7]
Database references
SIMBADdata

The visible component has a stellar classification of F2III,[3] matching an evolved star that has, at the age of age of 1.4 billion years,[5] become a giant. However, it has just 2.74[1] times the Sun's radius and shows a high rate of spin with a projected rotational velocity of +140 km/s.[3] The star has 1.76[5] times the mass of the Sun and is radiating 13[1] times the Sun's luminosity from its photosphere at an effective temperature of 6,848 K.[5]

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. Belle, G. T. (2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20: 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2.
  4. Ammler-von Eiff, M.; Reiners, A. (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724.
  5. Casagrande, L.; et al. (2011). "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey". Astronomy & Astrophysics. 530 (A138): 21. arXiv:1103.4651. Bibcode:2011A&A...530A.138C. doi:10.1051/0004-6361/201016276.
  6. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  7. "Lam Hor". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 March 2016.
  8. 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.
  9. Kunzli, M.; North, P. (January 1998). "Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F stars". Astronomy and Astrophysics Supplement. 127: 277–294. arXiv:astro-ph/9710226. Bibcode:1998A&AS..127..277K. doi:10.1051/aas:1998350.
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