Theta Cephei

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 127 light-years from Earth. The pair have an orbital period of 840.6 days with a low eccentricity of 0.03.[7] Shared with η Cep, this star system has the title Al Kidr.[10]

Theta Cephei
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cepheus
Right ascension  20h 29m 34.8652s[1]
Declination +62° 59′ 38.6216″[1]
Apparent magnitude (V) 4.22[2]
Characteristics
Spectral type A7 III[3]
U−B color index +0.16[2]
B−V color index +0.20[2]
Astrometry
Radial velocity (Rv)−6.8[4] km/s
Proper motion (μ) RA: 52.416[5] mas/yr
Dec.: −2.544[5] mas/yr
Parallax (π)25.7611 ± 0.5808[1] mas
Distance127 ± 3 ly
(38.8 ± 0.9 pc)
Absolute magnitude (MV)+1.12[6]
Orbit[7]
Period (P)840.6 d
Eccentricity (e)0.03
Periastron epoch (T)2416214.5 JD
Argument of periastron (ω)
(secondary)		83.7°
Semi-amplitude (K1)
(primary)		13.9 km/s
Details
θ Cep A
Luminosity28[8] L☉
Surface gravity (log g)3.74[3] cgs
Temperature7,816[3] K
Metallicity [Fe/H]+0.27±0.04[6] 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[9]
Database references
SIMBADdata

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.[11] Consequently, the Chinese name for θ Cephei itself is 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).[12]

References
  1. Brown, A. G. A. (2018), "Gaia Data Release 2. Summary of the contents and survey properties", Astronomy and Astrophysics, 616: A1, arXiv:1804.09365, Bibcode:2018A&A...616A...1G, doi:10.1051/0004-6361/201833051
  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. 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. Evans, D. S. (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. "tet Cep". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-05-06.
  10. Allen, Richard Hinckley (1963-06-01). Star Names: Their Lore and Meaning. Dover Publications. p. 155. ISBN 978-0486210797.
  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 6 日
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