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Gamma Cephei (γ Cep / γ Cephei) is a star in the constellation Cepheus. It also has the traditional name Alrai, also known as Errai (or Er Rai).
Gamma Cephei is a binary star approximately 50 light years from Earth, with an apparent magnitude of 3.22. The larger and brighter star is a stellar class K1 IV orange subgiant star. The smaller is a red dwarf in a poorly studied orbit: the current best guess is that it orbits eccentrically from 10 to 29 AU over the course of 70 yrs ± 16 yrs, with an eccentricity of 0.439 ± 0.06 (Cochran et al 2002).
Gamma Cephei is the naked-eye star that will follow Polaris as the Earth's northern pole star, due to the precession of the equinoxes. Alrai will become closer to the northern celestial pole than Polaris around 3000 AD, and be at its closest approach around 4000 AD. The "title" will pass to ι Cephei some time around 5200 AD.
The traditional name derives from the Arabic الراعي ar-rā‘ī, meaning "the shepherd". Confusingly, the star β Ophiuchi is sometimes also called Alrai, but it is more commonly known as Cebalrai or Kelb Alrai, meaning "shepherd's dog".
Planetary system
In 1989, a planet orbiting Gamma Cephei A was announced by Anthony Lawton and P. Wright. Its existence was also suspected by a Canadian team led by Bruce Campbell and Gordon Walker in the early 1990s. This would have been the first confirmed extrasolar planet, and it was hypothesized based on the same radial velocity technique later used successfully by others. However, the claim was retracted in 1992 due to the quality of the data not being good enough to make a solid discovery. But in 2002, evidence of the planet was considerably strengthened by the new measurements at the McDonald Observatory.
See also
References
External links
- McDonald Observatory: Planet Search finds first planet orbiting close-in binary star
- A Planetary Companion to the Binary Star Gamma Cephei
- SolStation: Errai 2
- Extrasolar Planets Encyclopaedia: Gamma Cephei + Gamma Cephei b
- Extrasolar Visions: Gamma Cephei A + Gamma Cephei Ab + Gamma cephei B
Bayer objects | Binary stars | Cepheus constellation | Flamsteed objects | Orange subgiants | Red dwarfs
"Gamma Cephei"