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
Distance 206 ± 3 ly
(63.2 ± 0.9 pc)
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
Luminosity 28[5] L
Surface gravity (log g) 3.74[3] cgs
Temperature 7,816[3] K
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[6]
Database references

Theta Cephei (θ Cep, 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.[4] Shared with η Cep, this star system has the title Al Kidr, meaning unknown[7]

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.[8] Consequently, θ Cephei itself is known as 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).[9]


  1. ^ a b c d e 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 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. ^ a b c d 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, Bibcode:2012PASJ...64...38T, doi:10.1093/pasj/64.2.38, 38 
  4. ^ a b Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, Bibcode:2004A&A...424..727P, arXiv:astro-ph/0406573Freely accessible, doi:10.1051/0004-6361:20041213. 
  5. ^ 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. 
  6. ^ "tet Cep -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-06. 
  7. ^ Allen, Richard Hinckley (1963-06-01). Star Names: Their Lore and Meaning. Dover Publications. p. 155. ISBN 978-0486210797. 
  8. ^ (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.
  9. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 6 日