Epsilon Tauri, formally named Ain, is an orange giantstar located approximately 45 parsecs from the Sun in the constellation of Taurus. An extrasolar planet is believed to be orbiting the star. It is a member of the Hyadesopen cluster. As such its age is well constrained at 625 million years. It is claimed to be the heaviest among planet-harboring stars with reliable initial masses although the star HD 13189 is potentially more massive. Given its large mass, this star, though presently of spectral type K0 III, was formerly of spectral type A that has now evolved off the main sequence into the giant phase. It is regarded as a red clump giant; that is, a core-helium burning star. Since Epsilon Tauri lies near the plane of the ecliptic, it is sometimes occulted by the Moon and by planets. It has an 11th magnitude companion 182 arcseconds from the primary.
Nomenclature
ε Tauri is the star's Bayer designation; it also bears the Flamsteed designation of 74 Tauri. On discovery, the planet was designated Epsilon Tauri b. The star bore the traditional name Ain and was given the name Oculus Boreus by John Flamsteed. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Ain for this star. In July 2014, the International Astronomical Union launched a process for giving proper names to certain exoplanets. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning name was Amateru for this planet. The winning name was based on that submitted by the Kamagari Astronomical Observatory of Kure, Hiroshima Prefecture, Japan: namely 'Amaterasu', the Shinto goddess of the Sun, born from the left eye of the god Izanagi. The IAU substituted 'Amateru' – which is a common Japanese appellation for shrines when they enshrine Amaterasu – because 'Amaterasu' is already used for an asteroid. In Chinese, 畢宿, meaning Net, refers to an asterism consisting ε Tauri, δ3 Tauri, δ1 Tauri, γ Tauri, Aldebaran, θ2 Tauri, 71 Tauri and λ Tauri. Consequently, the Chinese name for ε Tauri itself is 畢宿一, "the First Star of Net".
Planetary system
In 2007, a massive extrasolar planet was reported orbiting the star with a period of 1.6 years in a somewhat eccentric orbit. Its discoverers claimed it was the first planet ever discovered in an open cluster.
Epsilon Tauri is a major feature of the book Starsong Chronicles:Exodus, by American author JJ Clayborn. In the book, the star is referenced by the name Ain, but the characters rename the star Coronis. In Fred Saberhagen's Berserker series in the short storyPatron of the Arts, a human artist and a Berserker machine discuss the value of art and of this specific painting on a starship in the future after a space battle near the Sol system. In this short story, the Earth-Descended peoples place all of humanity's important artworks on an evacuation starship to preserve the works by sending them to Tau Epsilon.
