Alrai
|
|
Alrai, also known as Errai, Gamma Cephei, and HD 222404 is a double star approximately 50 light years from Earth, with an apparent magnitude of 3.22. Its name derives from the Arabic الراعي ar-rā‘ī, meaning "the shepherd".
The Alrai system consists of two stars. The larger and brighter is a class K1 IV orange subgiant star. The smaller is a red dwarf in a poorly studied orbit: current best guess is that it orbits eccentrically from 10 to 29 AU over the course of 70 years.
Alrai 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 star β Ophiuchi is sometimes also called Alrai, but it is more commonly known as Cebalrai or Kelb Alrai, meaning "shepherd's dog".
Alrai Ab
In 1989 a planet orbiting Alrai was announced by Anthony Lawton and P. Wright. 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 However, the claim was retracted in 1992. But in 2002, evidence of the planet was considerably strengthened by the new measurements at the McDonald Observatory. Alrai Ab orbits around Alrai A in about 902. Alrai Ab is also a Sulfur Giant.
External links
- McDonald Observatory Planet Search finds first planet orbiting close-in binary star (http://mcdonaldobservatory.org/news/releases/2002/1009.html) – McDonald Observatory Press Release (10/09/02)
- A Planetary Companion to the Binary Star Gamma Cephei (http://austral.as.utexas.edu/planets/gamcep/gamcep.html)de:Errai