Epsilon Indi

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Epsilon Indi is a K4 orange dwarf star some 12 light years away, it is the fifth brightest star of the constellation of Indus. The star is best known to astronomers as having the closest known Brown Dwarfs to our system.

Epsilon Indi, along with Epsilon Eridani were first mentioned in the celestial atlas known as the Uranometria by Johann Bayer in 1603[1].

The Star

Epsilon Indi is a orange-red main sequence star of spectral class K4-5 Ve. At first the star was believed to be considerably older then our Sun because of it's slow rotation. New observations though revealed the star has a much higher rotational speed, which now suggested that it may only be between one and two billion years old, with the age most likely around 1.3 billion years.

The star has some 77 percent of the mass of our Sun[2], and so 76 percent of its diameter[3]. Because it is a cooler class K star, Epsilon Indi is only 14.5 percent as luminous as our Sun. The metallicity of Epsilon Indi is estimated from 59 to 110 percent that of our Sun, based on its abundance of iron[4].

With an apparent magnitude of 4.69, Epsilon Indi can be seen by the unaided eye in dark skies with little light pollution.

Substellar Companions

On January 13, 2003 it was announced by astronomers, that they had discovered a class T brown dwarf orbiting Epsilon Indi[1]. Eight months later it was discovered that there was actually a second brown dwarf that orbited the first[5].

Epsilon Indi Ba

The more massive primary brown dwarf in the Epsilon Indi system, designated Epsilon Indi Ba, is classified as a spectral type T1V (methane) dwarf. The brown dwarf orbits Epsilon Indi at a distance of 1500 AU. It is estimated that Epsilon Indi Ba is some 47 times Jupiter's mass even though it has roughly the same diameter of Jupiter. The surface temperature is around 1,260K (in comparison, Epsilon Indi's surface temperature is 4300 K).

Epsilon Indi Bb

Epsilon Indi Bb orbits the larger Epsilon Indi Ba at a distance of some 2.65 AU. The cooler of the two, its spectral class is T6V with a surface temperature of 850K. It is also the lass massive of the two, with an estimate mass some 28 times of Jupiter.

There are no known planets orbiting Epsilon Indi at this time. The distance a planet would need to be to have liquid water on it's surface is centered around 0.38 AU from Epsilon Indi, or about the same distance Mercury is from our Sun.