Which exoplanet orbits the orange giant star Gamma Cephei A?

Gamma Cephei Ab is the exoplanet that orbits the orange giant star Gamma Cephei A.

Gamma Cephei A is a K-type giant or subgiant about 45 light-years away in the constellation Cepheus. It belongs to a binary system: a much fainter red dwarf, Gamma Cephei B, also orbits the primary. The planet is formally named Tadmor, a name chosen through the International Astronomical Union’s NameExoWorlds campaign.

The planet’s history is unusually important. Astronomers first reported evidence for it in 1988 using the radial-velocity method, which detects a star’s gravitational wobble. The original claim was withdrawn in 1992 because the observations were not secure, but improved measurements confirmed the planet in 2003. That makes it one of the earliest serious exoplanet discoveries.

Tadmor is a giant planet with a roughly 903-day orbit and a semimajor axis near 2 astronomical units. Its designation can cause confusion: “A” identifies the primary star, while the lowercase “b” identifies its first known planet.