Theta Cephei
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus[1] |
| Right ascension | 20h 29m 34.86518s[2] |
| Declination | +62° 59′ 38.6216″[2] |
| Apparent magnitude (V) | 4.22[3] |
| Characteristics | |
| Spectral type | A7 III[4] or kA7hF1mF2[5][6] |
| U−B color index | +0.16[3] |
| B−V color index | +0.20[3] |
| Astrometry | |
| Radial velocity (Rv) | −6.8[7] km/s |
| Proper motion (μ) | RA: 34.798 mas/yr[2] Dec.: −13.904 mas/yr[2] |
| Parallax (π) | 23.481±0.6894 mas[2] |
| Distance | 139 ± 4 ly (43 ± 1 pc) |
| Absolute magnitude (MV) | +1.12[1] |
| Orbit[8] | |
| Period (P) | 914.3±7.0 d |
| Eccentricity (e) | 0.377±0.006 |
| Periastron epoch (T) | 2456991.3±8.5 JD |
| Argument of periastron (ω) (primary) | 48.8±1.1° |
| Semi-amplitude (K1) (primary) | 7.72±0.06 km/s |
| Details | |
| primary | |
| Mass | 2.75[9] M☉ |
| Radius | 3.09+0.36 −0.25[10] R☉ |
| Luminosity | 46.5[9] L☉ |
| Surface gravity (log g) | 3.74[4] cgs |
| Temperature | 7,375+307 −404[10] K |
| Metallicity [Fe/H] | +0.27±0.04[1] dex |
| Rotational velocity (v sin i) | 52.0[4] km/s |
| Age | 55[9] Myr |
| companion | |
| Mass | >0.62[8] M☉ |
| Radius | 0.654+0.044 −0.102[8] R☉ |
| Temperature | 4,070+340 −130[8] K |
| Other designations | |
| θ Cep, 2 Cep, BD+62°1821, FK5 767, HD 195725, HIP 101093, HR 7850, SAO 18897[11] | |
| Database references | |
| SIMBAD | data |
Theta Cephei is a white-hued binary star system in the northern constellation of Cepheus. Its name is a Bayer designation that is Latinized from θ Cephei, and abbreviated Theta Cep or θ Cep. The system is visible to the naked eye as a point of light with an apparent visual magnitude of 4.22.[3] Based on parallax measurements, it is located at a distance of approximately 139 light-years (43 pc) from the Earth.
This is a spectroscopic binary star system with an orbital period of 2.5 years;[8] the eccentricity was long thought to be low, at 0.03,[12] but calculations published in 2020 have put it at a much higher 0.377.[8] They are separated by 4.16 AU.[13]
The primary component has a Stellar classification of A7III,[4] displaying as a metallic-line Am star.[5] At an estimated age of 55 million years,[9] it is spinning with a projected rotational velocity of 52 km/s.[4] The star has 2.75[9] times the mass of the Sun and three times the Sun's radius.[10] It is radiating 46.5[9] times the luminosity of the Sun from its photosphere at an effective temperature of 7,375 K.[10] 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.[9]
Shared with η Cep, this star system has the title Al Kidr.[14] 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.[15] Consequently, the Chinese name for θ Cephei itself is 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).[16]
References
- ^ a b c 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 XHIP record for this object at VizieR.
- ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023), "Gaia Data Release 3. Summary of the content and survey properties", Astronomy and Astrophysics, 674: A1, arXiv:2208.00211, Bibcode:2023A&A...674A...1G, doi:10.1051/0004-6361/202243940, S2CID 244398875 Gaia DR3 record for this source at VizieR.
- ^ 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): 99, Bibcode:1966CoLPL...4...99J.
- ^ a b c d e 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
- ^ a b 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.
- ^ 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.
- ^ 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.
- ^ a b c d e f Bischoff, Richard; et al. (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.
- ^ a b c d e f g Fouesneau, M.; et al. (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.
- ^ a b c d 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.
- ^ "tet Cep", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-05-06.
- ^ 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.
- ^ 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.
- ^ Allen, Richard Hinckley (2013) [June 1963], Star Names: Their Lore and Meaning, Dover Publications, p. 155, ISBN 978-0486210797
{{citation}}: CS1 maint: ignored ISBN errors (link) - ^ (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.
- ^ (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