Theta Cephei

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Theta Cephei
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cepheus
Right ascension 22h 26m 42.40624s[1]
Declination +78° 47′ 09.0725″[1]
Apparent magnitude (V) 4.22[2]
Spectral type A7 III[3]
U−B color index +0.16[2]
B−V color index +0.20[2]
Proper motion (μ) RA: −13.33[1] mas/yr
Dec.: −36.95[1] mas/yr
Parallax (π)15.83 ± 0.23[1] mas
Distance206 ± 3 ly
(63.2 ± 0.9 pc)
Absolute magnitude (MV)+1.12[4]
Period (P)840.6 d
Eccentricity (e)0.03
Periastron epoch (T)2416214.5 JD
Argument of periastron (ω)
Semi-amplitude (K1)
13.9 km/s
θ Cep A
Luminosity28[6] L
Surface gravity (log g)3.74[3] cgs
Temperature7,816[3] K
Metallicity [Fe/H]+0.27±0.04[4] dex
Rotational velocity (v sin i)52.0[3] km/s
Other designations
θ Cep, 2 Cep, BD+62° 1821, FK5 767, HD 195725, HIP 101093, HR 7850, SAO 18897[7]
Database references

Theta Cephei, Latinized from θ Cephei, is a stellar class A7, fourth-magnitude star in the constellation Cepheus. It is a white-hued, single-lined spectroscopic binary system, located about 206 light-years from Earth. The pair have an orbital period of 840.6 days with a low eccentricity of 0.03.[5] Shared with η Cep, this star system has the title Al Kidr.[8]

In Chinese, 天鈎 (Tiān Gōu), meaning Celestial Hook, refers to an asterism consisting of 4 Cephei, HD 194298, η Cephei, α Cephei, ξ Cephei, 26 Cephei, ι Cephei and ο Cephei.[9] Consequently, θ Cephei itself is known as 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).[10]


  1. 1.0 1.1 1.2 1.3 1.4 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. 2.0 2.1 2.2 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode 1966CoLPL...4...99J.
  3. 3.0 3.1 3.2 3.3 Takeda, Yoichi et al. (April 2012), "Lithium, Sodium, and Potassium Abundances in Sharp-Lined A-Type Stars", Publications of the Astronomical Society of Japan 64 (2): 15, arXiv:1111.1603, Bibcode 2012PASJ...64...38T, doi:10.1093/pasj/64.2.38, 38
  4. 4.0 4.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, arXiv:1108.4971, Bibcode 2012AstL...38..331A, doi:10.1134/S1063773712050015.
  5. 5.0 5.1 Pourbaix, D. et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics 424 (2): 727, arXiv:astro-ph/0406573, Bibcode 2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  6. McDonald, I. et al. (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.
  7. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  8. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  9. (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.
  10. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 6 日

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