Epsilon Indi

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**Epsilon Indi**
Observation data Epoch J2000.0 (ICRS)
Constellation	Indus
Right ascension	22^h 03^m 21.657^s
Declination	-56° 47′ 09.51″
Apparent magnitude (V)	4.68
Spectral Characteristics
Spectral type	K5Ve
U-B color index	1.00
B-V color index	1.05
Variable type	None
Astrometry
Radial velocity (R_v)	-40 km/s
Proper motion (μ)	RA: 3,961.41 mas/yr Dec.: -2,538.33 mas/yr
Parallax (π)	275.79 ± 0.69 mas
Distance	11.83 ± 0.03 ly (3.626 ± 0.009 pc)
Absolute magnitude (M_V)	6.88
Physical Characteristics
Mass	0.77 M_☉
Radius	0.76 R_☉
Luminosity	0.15 L_☉
Temperature	4,130 K
Metallicity	60-110%
Rotation	23 days (0.7 km/s)
Age	1.3 × 10⁹ years
Other designations
HD 209100, HR 8387, CP-57°10015, GCTP 5314.00, LHS 67, UGPMF 544

Epsilon Indi (ε Ind / ε Indi) is a star approximately 11.83 light years from Earth's solar system. This star has the second highest proper motion (second only to 61 Cygni) of any naked eye star, or possibly the third highest, since the magnitude 6.4 Groombridge 1830 is a naked eye star under exceptionally dark skies.

This star is suspected of being a member of a moving group of at least sixteen population I stars. ^[1] It has a space velocity relative to the Sun of 86 km/s.^[a] The surface gravity is:

log g = 4.65 ± 0.15

or slightly higher than the Sun.^[2]

As seen from Epsilon Indi, the Sun is a 2nd magnitude star in Ursa Major, near the bowl of the Big Dipper.^[b]

1 Companions
2 See also
3 Notes
4 References
5 External links

[edit] Companions

In January 2003, astronomers announced the discovery of a brown dwarf with a mass of 47 ± 10 Jupiter masses in orbit around Epsilon Indi at a distance of about 1500 AU. In August of 2003, astronomers discovered that this brown dwarf was actually a binary brown dwarf with a separation of about 2.5 AU. Both are of spectral class T; the larger brown dwarf has a mass of 47 ± 10 Jupiter masses, and the smaller 28 ± 7 Jupiter masses.^[3]^[4]

[edit] See also

[edit] Notes

a.	^{^} The space velocity components are: U = -77; V = -38, and W = +4. This yields a net space velocity of $\sqrt{77^2 + 38^2 + 4^2} = 86$ km/s.
b.	^{^} From Episilon Indi the Sun would appear on the diametrically opposite side of the sky at the coordinates RA=12^h 03^m 21^s, Dec=56° 47′ 10″, which is located near Delta Ursae Majoris. The absolute magnitude of the Sun is 4.8, so, at a distance of 3.63 parsecs, the Sun would have an apparent magnitude $m = M_v + 5\cdot((\log_{10} 3.63) - 1) = 2.6$ .

[edit] References

^ Eggen, O. J. (1971). "The zeta Herculis, sigma Puppis, ε Indi, and eta Cephei Groups of Old Disk Population Stars". Publications of the Astronomical Society of the Pacific 83 (493): 251-270.
^ Kollatschny, W. (1980). "A model atmosphere of the late type dwarf Epsilon INDI". Astronomy and Astrophysics 86 (3): 308-314.
^ K. Volk, R. Blum, G. Walker, P. Puxley (August, 2003). epsilon Indi B. IAU. Retrieved on 2006-11-29.
^ M. J. McCaughrean, L. M. Close, R.-D. Scholz, R. Lenzen, B. Biller, W. Brandner, M. Hartung, N. Lodieu (2004). "ε Indi Ba,Bb: The nearest binary brown dwarf". Astronomy and Astrophysics 413: 1029-1036.