Gamma Cephei
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 23h 39m 20.910s |
| Declination | +77° 37′ 56.51″ |
| Apparent magnitude (V) | 3.21 |
| Characteristics | |
| Gamma Cephei A | |
| Evolutionary stage | Red-giant branch |
| 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 |
| Name | 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 | 1.27+0.05 −0.07 M☉ |
| Radius | 4.74+0.03 −0.08 R☉ |
| Luminosity | 11.6±0.6 L☉ |
| Surface gravity (log g) | 3.18 cgs |
| Temperature | 4,806±60 K |
| Metallicity [Fe/H] | 0.20±0.07 dex |
| Rotational velocity (v sin i) | 1.63 km/s |
| Age | 5.7+0.8 −0.9 Gyr |
| Gamma Cephei B | |
| Mass | 0.328+0.009 −0.012 M☉ |
| Other designations | |
| Errai, γ Cep, 35 Cep, BD+76°928, FK5 893, GJ 903, HD 222404, HIP 116727, HR 8974, SAO 10818, PLX 5725.00 | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
Gamma Cephei is a binary star system in the northern constellation of Cepheus. Its name is a Bayer designation that is Latinized from γ Cephei, and abbreviated Gamma Cep or γ Cep. This system is visible to the naked eye as a point of light with a combined apparent visual magnitude of 3.21. Based on parallax measurements, it is located at a distance of approximately 45 light-years from Earth.
The primary, Gamma Cephei A, is officially named Errai, pronounced /ɛˈreɪ.iː/, the traditional name of the system. It is a stellar class K1 orange giant or subgiant star. The companion, Gamma Cephei B, is a low mass red dwarf star. A conformed exoplanet is orbiting the primary; it is designated Gamma Cephei Ab, later named Tadmor.
Gamma Cephei will succeed Polaris as the Earth's northern pole star, due to axial precession. It will be closer to the northern celestial pole than Polaris around 3157 CE and will make its closest approach around 4094 CE. The 'title' will pass to Iota Cephei some time around 5200 CE.