Gamma Cephei
 Location of γ Cephei (top center). |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Cepheus |
| Right ascension | 23h 39m 20.852s |
| Declination | +77° 37′ 56.19″ |
| Apparent magnitude (V) | 3.22 |
| Characteristics | |
| Gamma Cephei A | |
| Spectral type | K1IVe |
| U−B color index | 0.94 |
| B−V color index | 1.03 |
| Variable type | Suspected |
| Gamma Cephei B | |
| Spectral type | M4V |
| Astrometry | |
| Radial velocity (Rv) | 8.8 km/s |
| Proper motion (μ) |
RA: –47.96 ± 0.45 mas/yr Dec.: 126.59 ± 0.40 mas/yr |
| Parallax (π) | 72.69 ± 0.41mas |
| Distance | 44.9 ± 0.3 ly (13.76 ± 0.08 pc) |
| Absolute magnitude (MV) | 2.51 |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 67.5 ± 1.4 yr |
| Semi-major axis (a) | 1.467 ± 0.046" (20.18 ± 0.66 AU) |
| Eccentricity (e) | 0.4112 ± 0.0063 |
| Inclination (i) | 119.3 ± 1.0° |
| Longitude of the node (Ω) | 18.04 ± 0.98° |
| Periastron epoch (T) | 1991.605 ± 0.031 |
|
Argument of periastron (ω) (secondary) |
161.01 ± 0.40° |
| Details | |
| Gamma Cephei A | |
| Mass | 1.40 ± 0.12 M☉ |
| Radius | 4.79 ± 0.06 R☉ |
| Age | 6.6 Gyr |
| Gamma Cephei B | |
| Mass | 0.409 ± 0.018 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| Extrasolar Planets Encyclopaedia |
data |
Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the constellation of Cepheus. The primary (designated Gamma Cephei A, also named Errai) is a stellar class K1III-IV orange subgiant star; it has a red dwarf companion (Gamma Cephei B). An extrasolar planet (designated Gamma Cephei Ab, later named Tadmor) is believed to be orbiting the primary.
Gamma Cephei is the naked-eye star that will succeed Polaris as the Earth's northern pole star, due to the precession of the equinoxes. It will be closer to the northern celestial pole than Polaris around 3000 CE and will make its closest approach around 4000 CE. The 'title' will pass to Iota Cephei some time around 5200 CE.
Gamma Cephei has an apparent magnitude of 3.22, nearly all of which is accounted for by Gamma Cephei A. The primary is about 6.6 billion years old (based on Fe/H metallicity). and is on its first ascent off the main sequence. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.
Gamma Cephei B has a mass approximately 0.409 times that of the Sun. It is probably a red dwarf of class M4, 6.2 degrees of magnitude fainter than the primary. It is assumed to be of similar age to its primary.
γ Cephei (Latinised to Gamma Cephei) is the system's Bayer designation. Under the rules for naming objects in multiple star systems the two components are designated A and B. Following its discovery the planet was designated Gamma Cephei Ab.
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