Epsilon Indi

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Epsilon Indi
Observational Data
Designation HD 209100
HIP 108870
Right ascension 22h 03m 21.6571s
Declination −56o 47′ 09.514″
Constellation [[Indus]]
Type of object [[Star]]
Magnitude Apparent Mag: 4.69
Absolute Mag:6.89
Distance from Earth 11.83 ly
Radial velocity −40.4 km/s
Proper motion RA: 3,961.41 mas/yr
Dec.: −2,538.33 mas/yr
Parallax 275.79 ± 0.69 mas

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 was first mentioned in the celestial atlas known as the Uranometria by Johann Bayer in 1603.[1]

The Star

Epsilon Indi is an orange-red main sequence star of spectral class K4-5 Ve.

The star has some 77 percent of the mass of our Sun,[2] and some 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

Artist's conception of the Epsilon Indi system showing the star with its brown-dwarf binary companions. The relative sizes are not represented in this illustration.

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 also 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. 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 less massive of the two, with an estimated mass some 28 times that 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 its surface is centered around 0.38 AU from Epsilon Indi, or about the same distance Mercury is from our Sun.