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.[4] 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;[8] the eccentricity was long thought to be low, at 0.03,[11] but recent calculations have put it at a much higher 0.377.[8] They are separated by 4.16 AU.[12] 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]
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 20h 29m 34.86518s[1] |
| Declination | +62° 59′ 38.6216″[1] |
| Apparent magnitude (V) | 4.22[2] |
| Characteristics | |
| Spectral type | A7 III[3] or kA7hF1mF2[4][5] |
| U−B color index | +0.16[2] |
| B−V color index | +0.20[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.8[6] km/s |
| Proper motion (μ) | RA: 52.416[1] mas/yr Dec.: −2.544[1] mas/yr |
| Parallax (π) | 25.7611 ± 0.5808 mas[1] |
| Distance | 127 ± 3 ly (38.8 ± 0.9 pc) |
| Absolute magnitude (MV) | +1.12[7] |
| 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[1] R☉ |
| Luminosity | 46.5[9] L☉ |
| Surface gravity (log g) | 3.74[3] cgs |
| Temperature | 7,375+307 −404[1] K |
| Metallicity [Fe/H] | +0.27±0.04[7] dex |
| Rotational velocity (v sin i) | 52.0[3] 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 | |
| Database references | |
| SIMBAD | data |
Shared with η Cep, this star system has the title Al Kidr.[13] 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.[14] Consequently, the Chinese name for θ Cephei itself is 天鈎三 (Tiān Gōu sān, English: the Third Star of Celestial Hook.).[15]
References edit
- ^ a b c d e f g 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.
- ^ 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.
- ^ a b c 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 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.
- ^ a b c d e f 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.
- ^ a b c d 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.
- ^ "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 (1963-06-01), Star Names: Their Lore and Meaning, Dover Publications, p. 155, ISBN 978-0486210797
- ^ (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