Epsilon Aquilae

Epsilon Aquilae (ε Aql, ε Aquilae) is the Bayer designation for a binary star in the equatorial constellation of Aquila. It has an apparent visual magnitude of 4.02 and is visible to the naked eye. Based upon an annual parallax of 21.05 mas, Epsilon Aquilae lies at a distance of approximately 155 light-years (48 parsecs) from Earth. This is a spectroscopic binary system. The pair orbit each other over a period of 1,271 days (3.5 years) with an eccentricity of 0.27.

The primary component of this system is an evolved giant star with a stellar classification of K1 III. It has more than double the mass of the Sun and has expanded to ten times the Sun's radius. It shines with 54–fold the Sun's luminosity, which is being radiated from its outer envelope at an effective temperature of 4,760 K. At this heat, it glows with the orange-hue of a K-type star. This has been designated a barium star, meaning its atmosphere is extremely enriched with barium and other heavy elements. However, this is disputed, with astronomer Andrew McWilliam (1990) finding normal abundances from an s-process.