Epsilon Indi

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Epsilon Indi
Observation data
Epoch J2000.0 (ICRS)
Constellation
(pronunciation)		 Indus
Right ascension 22h 03m 21.6571s[1]
Declination −56° 47′ 09.514″[1]
Apparent magnitude (V) 4.69[1]
Characteristics
Spectral type K4.5 V[1]
U-B color index 1.00[2]
B-V color index 1.06[2]
Variable type None
Astrometry
Radial velocity (Rv) -40.4[1] km/s
Proper motion (μ) RA: 3,961.41[1] mas/yr
Dec.: -2,538.33[1] mas/yr
Parallax (π) 275.79 ± 0.69[1] mas
Distance 11.83 ± 0.03 ly
(3.626 ± 0.009 pc)
Absolute magnitude (MV) 6.88
Details
Mass 0.77[3] M☉
Radius 0.76[4] R☉
Surface gravity (log g) 4.65 ± 0.15[2]
Luminosity 0.15 L☉
Temperature 4,280[4] K
Metallicity 60-110%
Rotation 23 days (0.7 km/s)
Age 1.3 × 109[5] years
Other designations

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.

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

Contents

[edit] Properties

Epsilon Indi is a main sequence star with only about three-fourths the mass of the Sun.[3] Its surface gravity is slightly higher than the Sun's.[2] It has a space velocity relative to the Sun of 86 km/s,[b] and is suspected to be a member of a moving group of at least sixteen population I stars.[6]

In January 2003, astronomers announced the discovery of a brown dwarf with a mass of 40 to 60 Jupiter masses in orbit around Epsilon Indi at a distance of at least 1500 astronomical units.[7][8] In August 2003, astronomers discovered that this brown dwarf was actually a binary brown dwarf, with an apparent separation of 2.1 AU.[9] Both brown dwarfs are of spectral class T; the more massive, ε Indi Ba, has been classified as spectral type T1, while its less massive companion, ε Indi Bb, has been classified as spectral type T6. Evolutionary models[10] have been used to estimate their masses, radii and surface temperatures from spectroscopic and photometric measurements, giving masses of 47 ± 10 and 28 ± 7 Jupiter masses, radii of 0.091 ± 0.005 and 0.096 ± 0.005 solar radii, and temperatures of 1280 ± 40 K and 850 ± 20 K for ε Indi Ba and ε Indi Bb, respectively.[11]

[edit] Habitability

Epsilon Indi leads a list, compiled by Margaret Turnbull and Jill Tarter of the Carnegie Institution in Washington, of 17,129 nearby stars most likely to have planets that could support complex life.[12]

[edit] See also

[edit] Notes

a. ^  From Epsilon Indi the Sun would appear on the diametrically opposite side of the sky at the coordinates RA=10h 03m 21s, Dec=56° 47′ 10″, which is located near Beta 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.
b. ^ The space velocity components are: U = -77; V = -38, and W = +4.[2] This yields a net space velocity of \sqrt{77^2 + 38^2 + 4^2} = 86 km/s.

[edit] References

  1. ^ a b c d e f g h i SIMBAD Query Result: LHS 67 -- High proper-motion Star. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-07-11.
  2. ^ a b c d e Kollatschny, W. (1980). "A model atmosphere of the late type dwarf Epsilon INDI". Astronomy and Astrophysics 86 (3): 308-314. 
  3. ^ a b Staff (June 8, 2007). List of the Nearest 100 Stellar Systems. Research Consortium on Nearby Stars. Retrieved on 2007-07-11.
  4. ^ a b Johnson, H. M.; Wright, C. D. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun". Astrophysical Journal Supplement Series 53: 643-711. doi:10.1086/190905.  — see p. 701
  5. ^ Lachaume, R.; Dominik, C.; Lanz, T.; Habing, H. J. (1999). "Age determinations of main-sequence stars: combining different methods". Astronomy and Astrophysics 348: 897-909.  — This paper gives a median log age = 9.11, with a range of min = 8.91 and max = 9.31. This corresponds to 1.3 Gyr, with an error range of 0.8–2.0 Gyr.
  6. ^ 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. 
  7. ^ Discovery of Nearest Known Brown Dwarf: Bright Southern Star Epsilon Indi Has Cool, Substellar Companion, press release 01/03, European Southern Observatory, January 13, 2003. Accessed on line September 18, 2007.
  8. ^ ε Indi B: A new benchmark T dwarf, R.-D. Scholz, M. J. McCaughrean, N. Lodieu, and B. Kuhlbrodt, Astronomy and Astrophysics 398 (February 2003), pp. L29–L33.
  9. ^ K. Volk, R. Blum, G. Walker, P. Puxley (August 27, 2003). "epsilon Indi B". International Astronomical Union Circular (8188). IAU. 
  10. ^ E.g., Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458, I. Baraffe, G. Chabrier, T. Barman, F. Allard, and P. H. Hauschildt, Astronomy and Astrophysics 402 (May 2003), pp. 701–712.
  11. ^ M. J. McCaughrean et al (January 2004). "ε Indi Ba,Bb: The nearest binary brown dwarf". Astronomy and Astrophysics 413: 1029-1036. doi:10.1051/0004-6361:20034292. 
  12. ^ Stahl, Jason (January 2007). 20 Things You Didn't Know About... Aliens. Discover. Retrieved on 2007-03-02.

[edit] External links