Omega Capricorni

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Omega Capricorni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Capricornus
Right ascension 20h 51m 49.29084s[1]
Declination −26° 55′ 08.8574″[1]
Apparent magnitude (V) +4.11[2]
Spectral type K4 III[3]
U−B color index +1.93[2]
B−V color index +1.64[2]
Variable type Suspected[4]
Radial velocity (Rv)+9.1±1.4[5] km/s
Proper motion (μ) RA: −8.36[1] mas/yr
Dec.: −0.36[1] mas/yr
Parallax (π)3.87 ± 0.68[1] mas
Distanceapprox. 800 ly
(approx. 260 pc)
Absolute magnitude (MV)−2.7[6]
Mass6.8±0.9[7] M
Surface gravity (log g)0.85[8] cgs
Temperature3,960[8] K
Metallicity [Fe/H]−0.24[9] dex
Rotational velocity (v sin i)4.68[8] km/s
Age48.1±8.3[7] Myr
Other designations
 Cap, 18 Cap, CD−27° 15082, FK5 1546, HD 198542, HIP 102978, HR 7980, SAO 189781[10]
Database references

Omega Capricorni (ω Cap, ω Capricorni) is a star in the southern constellation Capricornus. It is visible to the naked eye, having an apparent visual magnitude of +4.11.[2] Based upon an annual parallax shift of 3.87 mas as seen from the Earth,[1] it is located approximately 800 light years from the Sun.

In Chinese, 天田 (Tiān Tián), meaning Celestial Farmland, refers to an asterism consisting of ω Capricorni, 3 Piscis Austrini, 24 Capricorni and ψ Capricorni.[11] Consequently, ω Capricorni itself is known as 天田二 (Tiān Tián èr, English: the First Star of Celestial Farmland.)[12]

This is an evolved K-type giant star with a stellar classification of K4 III,[3] and is a suspected variable.[4] It is a barium star,[6] showing an overabundance of the s-process elements. This suggests that Omega Capricorni has an orbiting white dwarf companion.[13] Based upon its properties and motion through space, it is a candidate member of the Ursa Major Moving Group[14] and has a relatively high peculiar velocity of 25.7±1.9 km/s, making it is a possible runaway star.[7]


  1. ^ a b c d e f 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. ^ a b c d Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N.
  3. ^ a b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan,
  4. ^ a b NSV 13351, American Association of Variable Star Observers, retrieved 2017-05-07.
  5. ^ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  6. ^ a b Mennessier, M. O.; et al. (October 1997), "Barium stars, galactic populations and evolution.", Astronomy and Astrophysics, 326: 722–730, Bibcode:1997A&A...326..722M.
  7. ^ a b c 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.
  8. ^ a b c Hekker, S.; Meléndez, J. (December 2007), "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters", Astronomy and Astrophysics, 475 (3): 1003–1009, arXiv:0709.1145, Bibcode:2007A&A...475.1003H, doi:10.1051/0004-6361:20078233.
  9. ^ McWilliam, Andrew (1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", The Astrophysical Journal Supplement Series, 74: 1075, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  10. ^ "ome Cap -- Variable Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-07.
  11. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  12. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
  13. ^ Gomez, A. E.; et al. (1997), "Absolute magnitudes and kinematics of barium stars", Astronomy and Astrophysics, 319: 881, Bibcode:1997A&A...319..881G.
  14. ^ Chupina, N. V.; et al. (June 2006), "Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars", Astronomy and Astrophysics, 451 (3): 909–916, Bibcode:2006A&A...451..909C, doi:10.1051/0004-6361:20054009. See table 7.