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Epsilon Indi

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Epsilon Indi
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Indus
Right ascension 22h 03m 21.6571s[1]
Declination −56° 47′ 09.514″[1]
Apparent magnitude (V) 4.69[1]
Characteristics
Spectral type K4.5V[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 mas[1]
Distance11.83 ± 0.03 ly
(3.626 ± 0.009 pc)
Absolute magnitude (MV)6.89[note 1]
Details
Mass0.77[3] M☉
Radius0.76[4] R☉
Luminosity (bolometric)0.17[note 2] L☉
Surface gravity (log g)4.65 ± 0.15[2] cgs
Temperature4,280[4] K
Metallicity[5]
Rotation23 days (0.7 km/s)
Age1.3 × 109[6] years
Other designations
CP(D) −57°10015, GCTP 5314.00, GJ 845, HD 209100, HIP 108870, HR 8387, LHS 67, SAO 247287, FK5 825, UGP 544.[1]
Database references
SIMBADdata

Epsilon Indi (ε Ind / ε Indi) is an orange dwarf star approximately 12 light-years away in the constellation of Indus. As seen from Epsilon Indi, the Sun is a 2nd magnitude star in Ursa Major, near the bowl of the Big Dipper.[note 3] As of 2003, two brown dwarfs were found orbiting the star.

Observation

The constellation Indus (the Indian) first appeared in Johann Bayer's celestial atlas Uranometria in 1603. The 1801 star atlas Uranographia, by German astronomer Johann Elert Bode, places Epsilon Indi as one of the arrows being held in the left hand of the Indian.[7]

In 1847, Heinrich Louis d'Arrest compared the position of this star in several catalogues dating back to 1750, and discovered that it possessed a measureable proper motion. That is, he found that the star had changed position across the celestial sphere over time.[8] In 1882-3, the parallax of Epsilon Indi was measured by astronomers David Gill and William L. Elkin at the Cape of Good Hope. They derived a parallax estimate of .22±.03 arcseconds.[9] In 1923, Harlow Shapley of the Harvard Observatory derived a parallax of 0.45 arcseconds.[10]

During Project Ozma in 1960, this star was examined for artificial radio signals, but none were found.[11] In 1972, the Copernicus satellite was used to examine this star for the emission of ultraviolet laser signals. Again, the result was negative.[12] 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.[13]

Characteristics

Epsilon Indi is a dwarf star of spectral type K4.5V. The star has only about three-fourths the mass of the Sun.[3] Its surface gravity is slightly higher than the Sun's.[2] The metallicity of a star is the proportion of elements with higher atomic numbers than helium, being typically represented by the ratio of iron to hydrogen compared to the same ratio for the Sun; Epsilon Indi is found to have about 79% of the Sun's proportion of Iron in its photosphere.[5]

The corona of Epsilon Indi is similar to the Sun, with an X-ray luminosity Lx = 2×1027 ergs s-1 and an estimated coronal temperature of 2×106 K. The stellar wind of this star expands outward, producing a bow shock at a distance of 63 AU. Downstream of the bow, the termination shock reaches as far as 140 AU from the star.[14]

This star has the third highest proper motion of any star visible to the unaided eye (after Groombridge 1830 and 61 Cygni)[15] and the ninth highest overall.[16] It has a space velocity relative to the Sun of 86 km/s,[note 4][2] This yields a net space velocity of  km/s.</ref> which is unusually high for what is considered a young star.[17] It is thought to be a member of the ε Indi moving group of at least sixteen population I stars.[18] This is an association of stars that have similar space velocity vectors, and therefore most likely formed at the same time and location.[19]

Companions

Artist's conception of the Epsilon Indi system showing Epsilon Indi and the brown-dwarf binary companions.

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 1,500 astronomical units.[20][21] In August 2003, astronomers discovered that this brown dwarf was actually a binary brown dwarf, with an apparent separation of 2.1 AU.[22] Both brown dwarfs are of spectral class T; the more massive, ε Indi Ba, has been classified as spectral type T1V, while its less massive companion, Epsilon Indi Bb, has been classified as spectral type T6V.

Evolutionary models[23] have been used to estimate the physical properties of these brown dwarfs from spectroscopic and photometric measurements. These yield masses of 47 ± 10 and 28 ± 7 times the mass of Jupiter, radii of 0.091 ± 0.005 and 0.096 ± 0.005 solar radii, and effective temperature of 1280 ± 40 K and 850 ± 20 K for Epsilon Indi Ba and Epsilon Indi Bb, respectively.[24]

Measurements of the radial velocity of Epsilon Indi appear to show a trend that indicated the presence of a planetary companion with an orbital period of more than 20 years. A visual search using the ESO's Very Large Telescope found one potential candidate. However, a subsequent examination by the Hubble Space Telescope NICMOS showed that this was a background object. Thus, no other companions have yet been found orbiting this star.[25]

See also

Notes

  1. ^ From apparent visual magnitude and parallax.
  2. ^ From L=4πR2σTeff4, where L is the luminosity, R is the radius, Teff is the effective surface temperature and σ is the Stefan–Boltzmann constant.
  3. ^ 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 .
  4. ^ The space velocity components are: U = -77; V = -38, and W = +4.

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 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). Retrieved 2007-07-11. {{cite journal}}: Unknown parameter |ages= ignored (help)
  3. ^ a b Staff (2007-06-08). "List of the Nearest 100 Stellar Systems". Research Consortium on Nearby Stars. Retrieved 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. Retrieved 2007-07-11.{{cite journal}}: CS1 maint: multiple names: authors list (link) — see p. 701
  5. ^ a b Kotoneva, Eira (2002). "Luminosity-metallicity relation for stars on the lower main sequence". Monthly Notices of the Royal Astronomical Society. 335 (4): 1147–1157. Retrieved 2008-07-01. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ 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. Retrieved 2007-07-12.{{cite journal}}: CS1 maint: multiple names: authors list (link) — 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.
  7. ^ Scholz, Ralf-Dieter (2003-01-13). "Discovery of Nearest Known Brown Dwarf". ESO. Retrieved 2008-07-02. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ D'Arrest, M. (1847). "On proper motion of ε Indi". Monthly Notices of the Royal Astronomical Society. 8: 16. Retrieved 2008-07-01.
  9. ^ Callandreau, O. (1886). "Revue des publications astronomiques. Heliometer determinations of Stellar parallax, in the southern hemisphere, by David Gill and W. L. Elkin". Bulletin Astronomique (in French). 2 (1): 42–44. Retrieved 2008-07-01.
  10. ^ Shapley, Harlow (1923). "Epsilon Indi". Harvard College Observatory Bulletin (789): 2. Retrieved 2008-07-02.
  11. ^ Burnham, Robert (1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System. Courier Dover Publications. ISBN 0486235688. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Lawton, A. T. (1975). "CETI from Copernicus". Spaceflight. 17: 328–330. Retrieved 2008-07-02.
  13. ^ Stahl, Jason (2007). "20 Things You Didn't Know About... Aliens". Discover. Retrieved 2007-03-02. {{cite web}}: Unknown parameter |month= ignored (help)
  14. ^ Müller, Hans-Reinhard (2001). "Modeling the Interstellar Medium-Stellar Wind Interactions of λ Andromedae and ε Indi". The Astrophysical Journal. 551: 495–506. doi:10.1086/320070. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ Weaver, Harold F. (1947). "The Visibility of Stars Without Optical Aid". Publications of the Astronomical Society of the Pacific. 59 (350): 232–243. Retrieved 2007-02-04.
  16. ^ Staff (2007-05-04). "High Proper Motion Stars: Interesting Areas to View". ESA. Retrieved 2006-08-10.
  17. ^ Rocha-Pinto, Helio J. (2001). "Chromospherically Young, Kinematically Old Stars". Astrophysical Ages and Times Scales. Astronomical Society of the Pacific. pp. 364-. Retrieved 2007-01-08. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  18. ^ 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.
  19. ^ Kollatschny, W. (1980). "A model atmosphere of the late type dwarf Epsilon INDI". Astronomy and Astrophysics. 86 (3): 308–314. Retrieved 2008-07-01.
  20. ^ Scholz, Ralf-Dieter (2003-01-13). "Discovery of Nearest Known Brown Dwarf: Bright Southern Star Epsilon Indi Has Cool, Substellar Companion". European Southern Observatory. Retrieved 2006-05-24. {{cite news}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  21. ^ Scholz, R.-D. (2003). "ε Indi B: A new benchmark T dwarf". Astronomy and Astrophysics. 398: L29–L33. Retrieved 2008-06-24. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  22. ^ Volk, K. (2003). "epsilon Indi B". International Astronomical Union Circular (8188). IAU. Retrieved 2006-11-29. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  23. ^ E.g., Baraffe, I. (2003). "Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458". Astronomy and Astrophysics. 402: 701–712. Retrieved 2008-06-24. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  24. ^ McCaughrean, M. J.; et al. (2004). "ε Indi Ba, Bb: The nearest binary brown dwarf". Astronomy and Astrophysics. 413: 1029–1036. doi:10.1051/0004-6361:20034292. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)
  25. ^ Geißler, K. (2007). "A direct and differential imaging search for sub-stellar companions to epsilon Indi A". Astronomy and Astrophysics. 461 (2): 665–668. Retrieved 2008-07-02. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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