Eta Arae

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Eta Arae
Diagram showing star positions and boundaries of the Ara constellation and its surroundings
Cercle rouge 100%.svg

The location of η Arae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ara
Right ascension 16h 49m 47.15653s[1]
Declination –59° 02′ 28.9575″[1]
Apparent magnitude (V) 3.76[2]
Spectral type K5 III[3]
U−B color index +1.93[2]
B−V color index +1.57[2]
Radial velocity (Rv) +9.0[4] km/s
Proper motion (μ) RA: +39.73[1] mas/yr
Dec.: –24.91[1] mas/yr
Parallax (π) 10.90 ± 0.20[1] mas
Distance 299 ± 5 ly
(92 ± 2 pc)
Absolute magnitude (MV) –1.14 ± 0.14[5]
Mass 1.02 ± 0.12[5] M
Radius 55.9 ± 7.3[5] R
Surface gravity (log g) 0.92 ± 0.12[5] cgs
Temperature 3,886[5] K
Metallicity [Fe/H] –0.37[5] dex
Age 7.11 ± 2.34[5] Gyr
Other designations
CPD–58° 6906, FK5 1435, HD 151249, HIP 82363, HR 6229, SAO 244168.[6]
Database references

Eta Arae (η Ara, η Arae) is the Bayer designation for a single [7] star in the southern constellation of Ara. It is approximately 299 light-years (92 parsecs) from Earth and is visible to the naked eye with an apparent visual magnitude of 3.76.[2]

The spectrum of this star matches a stellar classification of K5 III,[3] indicating that, at an estimated age of seven billion years,[5] it has reached the giant star stage of its evolution. With a mass nearly the same as the Sun, it has an outer envelope that has expanded to nearly 56 times the Sun's radius.[5] The star is now spinning so slowly that it takes more than eleven years to complete a single rotation.[8] Eta Arae is radiating energy into space at an effective temperature of 3,886 K,[5] giving it the orange-hued glow of a K-type star.[9]

It has a 14th magnitude optical companion, located 25.7 arcseconds away.


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J. 
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  4. ^ Wilson, Ralph Elmer (1953), General catalogue of stellar radial velocities, Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  5. ^ a b c d e f g h i j da Silva, L.; et al. (November 2006), "Basic physical parameters of a selected sample of evolved stars", Astronomy and Astrophysics, 458 (2): 609–623, arXiv:astro-ph/0608160Freely accessible, Bibcode:2006A&A...458..609D, doi:10.1051/0004-6361:20065105. 
  6. ^ "eta Ara -- Star in double system", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-27. 
  7. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  8. ^ Setiawan, J.; et al. (July 2004), "Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch", Astronomy and Astrophysics, 421: 241–254, Bibcode:2004A&A...421..241S, doi:10.1051/0004-6361:20041042-1. 
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-06-24. 

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