Theta Cephei

Theta Cephei
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]
Distance127 ± 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
Mass2.75[9] M☉
Radius3.09+0.36
−0.25[1] R☉
Luminosity46.5[9] L☉
Surface gravity (log g)3.74[3] cgs
Temperature7,375+307
−404[1] K
Metallicity [Fe/H]+0.27±0.04[7] dex
Rotational velocity (v sin i)52.0[3] km/s
Age55[9] Myr
companion
Mass>0.62[8] M☉
Radius0.654+0.044
−0.102[8] R☉
Temperature4,070+340
−130[8] K
Other designations
θ Cep, 2 Cep, BD+62°1821, FK5 767, HD 195725, HIP 101093, HR 7850, SAO 18897[10]
Database references
SIMBADdata

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]

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]

  1. ^ a b c d e f g Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference Johnson1966 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Takeda2012 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Abt_Morrell_1995 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference mk was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference rv was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  8. ^ a b c d e f Cite error: The named reference Bischoff was invoked but never defined (see the help page).
  9. ^ a b c d Cite error: The named reference fouesneau2022 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Abt1961 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Trilling_et_al_2007 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference allen1963 was invoked but never defined (see the help page).
  14. ^ (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.
  15. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 6 日