The primary (designated Gamma Cephei A, officially named Errai /ɛˈreɪ.iː/, the traditional name of the system)[11][12] 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.

[8] The primary is about 5.7 billion years old and has evolved off the main sequence, having fused all of the hydrogen in its core.

Under the rules for naming objects in multiple star systems the two components are designated A and B.

The system bore a traditional name variously spelled as Errai, Er Rai or Alrai, deriving from the Arabic الراعي (ar-rā‘ī), meaning 'the shepherd'.

In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets.

[25] This was the first-discovered extrasolar planet and its ostensible discovery was based on the same radial velocity technique later used successfully by others.

[27] Astrometric measurements have shown that the planet's orbital inclination is between 3.7° and 15.5°, meaning that its true mass is between 6.6 and 28.1 MJ.