Star in the constellation Cepheus From Wikipedia, the free encyclopedia
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]
Seamless Wikipedia browsing. On steroids.