Theta Capricorni

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Theta Capricorni
Diagram showing star positions and boundaries of the Capricornus constellation and its surroundings
Cercle rouge 100%.svg

Location of θ Capricorni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Capricornus
Right ascension 21h 05m 56.82783s[1]
Declination −17° 13′ 58.3021″[1]
Apparent magnitude (V) +4.07[2]
Spectral type A1 V[3]
U−B color index +0.01[2]
B−V color index −0.01[2]
Proper motion (μ) RA: +79.33[1] mas/yr
Dec.: −62.01[1] mas/yr
Parallax (π) 20.11 ± 0.28[1] mas
Distance 162 ± 2 ly
(49.7 ± 0.7 pc)
Mass 2.24 M
Radius 2.7[5] R
Luminosity 65[6] L
Surface gravity (log g) 4.19±0.14 cgs
Temperature 10,001±340 K
Rotational velocity (v sin i) 104 km/s
Age 152 Myr
Other designations
θ Cap, 23 Cap, BD−17° 6174, FK5 1552, HD 200761, HIP 104139, HR 8075, SAO 164132[7]
Database references

Theta Capricorni (θ Cap, θ Capricorni) is a white-hued star in the southern constellation of Capricornus, located about a half degree south of the ecliptic.[8] Sometimes, this star is called by the name Dorsum,[9] meaning the back (of the goat) in Latin. It can be seen with the naked eye, having an apparent visual magnitude of +4.07.[2] Based upon an annual parallax shift of 20.11 mas as seen from the Earth,[1] the star is located about 162 light years from the Sun.

This is an A-type main sequence star with a stellar classification of A1 V.[3] It displays radial velocity variations that indicate it may be a binary star system.[10] However, when the system was examined in the infrared, no companion was detected.[11] Theta Capricorni has an estimated 2.24[4] times the mass of the Sun and around 2.7[5] times the Sun's radius. It is 152 million years old and is spinning fairly rapidly with a projected rotational velocity of 104 km/s.[4] It is radiating 65[6] times the solar luminosity from its photosphere at an effective temperature of around 10,000 K.[4]

Chinese name[edit]

In Chinese, 十二國 (Shíer Guó), meaning Twelve States, refers to an asterism which represents twelve ancient states in the Spring and Autumn period and the Warring States period, consisting of θ Capricorni, φ Capricorni, ι Capricorni, 38 Capricorni, 35 Capricorni, 36 Capricorni, χ Capricorni, 30 Capricorni, 33 Capricorni, ζ Capricorni, 19 Capricorni, 26 Capricorni, 27 Capricorni, 20 Capricorni, η Capricorni and 21 Capricorni.[12] Consequently, θ Capricorni itself is known as 秦一 (Qin yī, English: the First Star of Qin), meaning that this star (together with 30 Capricorni and δ Serpentis in Right Wall of Heavenly Market Enclosure (asterism)[13]) represents the state Qin () (or Tsin)[14]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d 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. ^ a b Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819. 
  4. ^ a b c d 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, Bibcode:2015ApJ...804..146D, arXiv:1501.03154Freely accessible, doi:10.1088/0004-637X/804/2/146. 
  5. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367: 521–524, Bibcode:2001A&A...367..521P, arXiv:astro-ph/0012289Freely accessible, doi:10.1051/0004-6361:20000451. 
  6. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, Bibcode:2012MNRAS.427..343M, arXiv:1208.2037Freely accessible, doi:10.1111/j.1365-2966.2012.21873.x. 
  7. ^ "tet Cap -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-15. 
  8. ^ Kaler, James B. (September 12, 2008), "Theta Capricorni", Stars, University of Illinois, retrieved 2017-05-09. 
  9. ^ "Dorsum",, retrieved 2017-05-16. 
  10. ^ Lagrange, A.-M.; et al. (February 2009), "Extrasolar planets and brown dwarfs around A-F type stars. VI. High precision RV survey of early type dwarfs with HARPS", Astronomy and Astrophysics, 495 (1): 335–352, Bibcode:2009A&A...495..335L, arXiv:0809.4636Freely accessible, doi:10.1051/0004-6361:200810105. 
  11. ^ Ehrenreich, D.; et al. (November 2010), "Deep infrared imaging of close companions to austral A- and F-type stars", Astronomy and Astrophysics, 523: A73, Bibcode:2010A&A...523A..73E, arXiv:1007.0002Freely accessible, doi:10.1051/0004-6361/201014763. 
  12. ^ (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.
  13. ^ "LacusCurtius • Allen's Star Names — Serpens". 
  14. ^ Allen, Richard Hinckley (1963), "Capricornus", Star Names, Their Lore and Meaning, Dover, retrieved 2017-05-09.