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 |
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]
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 |
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]