Alpha Horologii

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Alpha Horologii
Observation data
Epoch J2000      Equinox J2000
Constellation Horologium
Right ascension 04h 14m 00.11445s[1]
Declination −42° 17′ 39.7232″ [1]
Apparent magnitude (V) +3.853[2]
Spectral type K2 III[3]
U−B color index +1.013[2]
B−V color index +1.097[2]
Radial velocity (Rv)+21.6±0.3[4] km/s
Proper motion (μ) RA: +42.0±0.11[1] mas/yr
Dec.: −203.55±0.12[1] mas/yr
Parallax (π)28.36 ± 0.12 mas[1]
Distance115.0 ± 0.5 ly
(35.3 ± 0.1 pc)
Absolute bolometric
Mass1.55[5] M
Luminosity37.61[6] L
Temperature5,028[6] K
Metallicity [Fe/H]-0.02[5] dex
Other designations
α Hor, CD−42° 1425, HD 26967, HIP 19747, HR 1326, SAO 216710[7]
Database references

Alpha Horologii (α Horologii) is a solitary[8] orange-hued giant star in the constellation Horologium. It is visible to the naked eye with an apparent visual magnitude of +3.85.[2] Based upon an annual parallax shift of 28.36 mas as seen from the Earth, it is located 115.0±0.5 light-years from the Sun. The star is moving away from the Sun with a radial velocity of +21.6 km/s.[4]

The stellar classification of K2 III[3] indicates this is an evolved giant star of the K class. This means it has consumed the hydrogen at its core and has migrated away from the main sequence, with its outer envelope cooling and expanding in the process. Alpha Horologii has an estimated 1.55[5] times the mass of the Sun and is radiating 38[6] times the Sun's luminosity from its photosphere at an effective temperature of 5,028 K.[6] It has swollen to around 11 times the diameter of the Sun, having spent much of its life as a white main sequence star.[9]


  1. ^ a b c d e 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. S2CID 18759600.
  2. ^ a b c d Cousins, A. W. J. (1973), "Revised zero points and UBV photometry of stars in the Harvard E and F regions", Memoirs of the Royal Astronomical Society, 77: 223–236, Bibcode:1973MmRAS..77..223C.
  3. ^ a b Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 250741593.
  4. ^ a b de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  5. ^ a b c d Liu, Y. J.; Zhao, G.; Shi, J. R.; Pietrzyński, G.; Gieren, W. (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.
  6. ^ a b c d McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012). "Fundamental Parameters and Infrared Excesses of Hipparcos Stars". Monthly Notices of the Royal Astronomical Society. 427 (1): 343–57. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. S2CID 118665352.
  7. ^ "Alpha Horologii". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 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, S2CID 14878976.
  9. ^ Kaler, Jim. "Alpha Horologii". James Kaler's Stars. Retrieved 20 September 2019.