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Theta Cephei, Latinized from θ Cephei, is a stellar class A7, fourth-magnitude star in the constellation Cepheus. This displays at a metallic-line Am star. It is a white-hued, single-lined spectroscopic binary system, located about 127 light-years from Earth. The pair have an orbital period of 2.5 years; the eccentricity was long thought to be low, at 0.03, but recent calculations have put it at a much higher 0.377. They are separated by 4.16 AU. The companion star is calculated to be about 400 times fainter than the primary. It is completely invisible in the spectrum, but is estimated to be a K7 main sequence star.

Shared with η Cep, this star system has the title Al Kidr. 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. Consequently, the Chinese name for θ Cephei itself is 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).

References

1. ^ Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
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. ^ Abt, Helmut A.; Morrell, Nidia I. (1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", The Astrophysical Journal Supplement Series, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
5. Skiff, B. A (2014), "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)", VizieR On-line Data Catalog: B/Mk. Originally Published in: Lowell Observatory (October 2014), 1, Bibcode:2014yCat....1.2023S.
6. 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.
7. ^ 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, S2CID 119257644.
8. ^ Bischoff, Richard; Mugrauer, Markus; Lux, Oliver; Zehe, Tamara; Heyne, Therese; Wagner, Daniel; Geymeier, Michael (2020), "Spectroscopic orbit determination of the long periodic binary system θ Cep", Astronomische Nachrichten, 341 (10): 989, arXiv:2011.05241, Bibcode:2020AN....341..989B, doi:10.1002/asna.202013850, S2CID 229394315.
9. ^ Fouesneau, M.; Andrae, R.; Dharmawardena, T.; Rybizki, J.; Bailer-Jones, C. A. L.; Demleitner, M. (2022), "Astrophysical parameters from Gaia DR2, 2MASS, and AllWISE", Astronomy and Astrophysics, 662: A125, arXiv:2201.03252, Bibcode:2022A&A...662A.125F, doi:10.1051/0004-6361/202141828, S2CID 245837778.
10. "tet Cep", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-05-06.
11. Abt, Helmut A. (March 1961), "The Frequency of Binaries among Metallic-Line Stars", Astrophysical Journal Supplement, 6: 37, Bibcode:1961ApJS....6...37A, doi:10.1086/190060.
12. Trilling, D. E.; et al. (April 2007), "Debris disks in main-sequence binary systems", The Astrophysical Journal, 658 (2): 1264–1288, arXiv:astro-ph/0612029, Bibcode:2007ApJ...658.1289T, doi:10.1086/511668, S2CID 14867168.
13. Allen, Richard Hinckley (1963-06-01), Star Names: Their Lore and Meaning, Dover Publications, p. 155, ISBN 978-0486210797
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15. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 6 日 Archived 2011-07-16 at the Wayback Machine

v t e Constellation of Cepheus
List of stars in Cepheus Cepheus in Chinese astronomy
Stars	Bayer α (Alderamin) β (Alfirk) γ (Errai) δ ε ζ η θ ι κ λ μ (Garnet Star) ν ξ (Kurhah) ο π ρ ρ Flamsteed 7 9 11 14 16 19 24 2 UMi Variable AR T V W RW VV VW WZ DH DO MY PV S SS ST U V354 V381 V419 HR 597 881 7955 8281 8442 8702 8748 8938 9038 HD 1 197911 204521 Other Gliese 809 WISE 0313+7807 WR 156 IRAS 23077+6707
Exoplanets γ Cephei Ab (Tadmor) TOI-1431 b
Star clusters	NGC 188 6939 7023 7129 7142 7160 7380 7419 7429 7510 Other Palomar 1
Nebulae	NGC NGC 40 NGC 7129 NGC 7139 NGC 7354 NGC 7538 NGC 7822 Other Seahorse Nebula Elephant's Trunk Nebula Ghost Nebula Gyulbudaghian's Nebula IC 1396 Iris Nebula L1157 S 155 SSTGFLS J222557+601148
Galaxies	NGC 2276 2300 6952 Other 3C 61.1 S5 0014+81 NVSS 2146+82 UGC 11861
Category

• A-type giants
• Am stars
• Spectroscopic binaries
• Cepheus (constellation)
• Bayer objects
• Durchmusterung objects
• Flamsteed objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Bright Star Catalogue objects