Gamma Cephei
Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the northern constellation of Cepheus. The primary (designated Gamma Cephei A, officially named Errai /ɛˈreɪ.iː/, the traditional name of the system) is a stellar class K1 orange giant or subgiant star; it has a red dwarf companion (Gamma Cephei B). An exoplanet (designated Gamma Cephei Ab, later named Tadmor) has been confirmed to be orbiting the primary.
Location of γ Cephei (top center) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 23h 39m 20.910s |
| Declination | +77° 37′ 56.51″ |
| Apparent magnitude (V) | 3.21 |
| Characteristics | |
| Gamma Cephei A | |
| Spectral type | K1III-IV CN1 |
| 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) | −42.82±0.30 km/s |
| Proper motion (μ) | RA: –64.860 mas/yr Dec.: 171.159 mas/yr |
| Parallax (π) | 72.5167 ± 0.1470 mas |
| Distance | 44.98 ± 0.09 ly (13.79 ± 0.03 pc) |
| Absolute magnitude (MV) | 2.62 |
| Orbit | |
| Primary | A |
| Companion | B |
| Period (P) | 66.84±1.32 yr |
| Semi-major axis (a) | 1.419±0.012" (19.56±0.18 AU) |
| Eccentricity (e) | 0.4144±0.0066 |
| Inclination (i) | 120.18±0.27° |
| Longitude of the node (Ω) | 18.32±0.78° |
| Periastron epoch (T) | 1991.581±0.048 |
| Argument of periastron (ω) (secondary) | 340.49±0.50° |
| Semi-amplitude (K1) (primary) | 1.898±0.014 km/s |
| Details | |
| Gamma Cephei A | |
| Mass | 1.294±0.081 M☉ |
| Radius | 4.93±0.04 R☉ |
| Luminosity | 11.6±0.6 L☉ |
| Surface gravity (log g) | +3.18 cgs |
| Temperature | 4,792±62 K |
| Metallicity [Fe/H] | −0.05 dex |
| Rotational velocity (v sin i) | 1.63 km/s |
| Age | 3.25±0.63 Gyr |
| Gamma Cephei B | |
| Mass | 0.384±0.013 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
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.