Omega Eridani

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ω Eridani
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 04h 52m 53.66995s[1]
Declination −05° 27′ 09.6972″[1]
Apparent magnitude (V) 4.37[2]
Spectral type A9 IVn[3]
U−B color index +0.12[2]
B−V color index +0.26[2]
Radial velocity (Rv) −8.3[4] km/s
Proper motion (μ) RA: −17.86[1] mas/yr
Dec.: +25.57[1] mas/yr
Parallax (π) 13.88 ± 0.24[1] mas
Distance 235 ± 4 ly
(72 ± 1 pc)
Absolute magnitude (MV) 0.10[5]
Period (P) 3,057 d
Eccentricity (e) 0.46
Periastron epoch (T) 2419973.0 JD
Argument of periastron (ω)
Semi-amplitude (K1)
18.1 km/s
Radius 6.7[7] R
Luminosity 69[8] L
Surface gravity (log g) 3.4[5] cgs
Temperature 6,878[8] K
Metallicity [Fe/H] 0.18[5] dex
Rotational velocity (v sin i) 186[9] km/s
Other designations
ω Eri, BD−05° 1068, 61 Eridani, HD 31109, HIP 22701, HR 1560, SAO 131568.[10]
Database references

Omega Eridani (ω Eri) is a binary star[9] system in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude is 4.37.[2] The distance to this star, as determined by the parallax method, is around 235 light years.

This is a single-lined spectroscopic binary[11] system with an orbital period of 3,057 days (8.4 years) and an eccentricity of 0.46. The primary component is an A-type subgiant star with a stellar classification of A9 IVn,[3] where the 'n' suffix indicates a broad ("nebulous") absorption due to rotation. The projected rotational velocity is 186[9] km/s.[9] This is giving the star an oblate shape with an equator that is 13% wider than the polar radius. The angular size of Omega Eridani is 0.87 mas.[12] At an estimated distance of the star, this yields a physical size of around 6.7 times the radius of the Sun.[7]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Abt, Helmut A.; Morrell, Nidia I. (July 1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182. 
  4. ^ De Bruijne, J. H. J.; Eilers, A.-C. (2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: A61, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219. 
  5. ^ a b c Giridhar, S.; et al. (August 2013), "Identification of metal-poor stars using the artificial neural network", Astronomy & Astrophysics, 556: 11, Bibcode:2013A&A...556A.121G, arXiv:1307.6308Freely accessible, doi:10.1051/0004-6361/201219918, A121. 
  6. ^ Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727–732, Bibcode:2004A&A...424..727P, arXiv:astro-ph/0406573Freely accessible, doi:10.1051/0004-6361:20041213. 
  7. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1.  The radius (R*) is given by:
  8. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, Bibcode:2012MNRAS.427..343M, arXiv:1208.2037Freely accessible, doi:10.1111/j.1365-2966.2012.21873.x. 
  9. ^ a b c d Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, Bibcode:2007A&A...463..671R, arXiv:astro-ph/0610785Freely accessible, doi:10.1051/0004-6361:20065224. 
  10. ^ "* ome Eri -- Spectroscopic binary". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-11-03. 
  11. ^ Abt, Helmut A.; Boonyarak, Chayan (November 2004), "Tidal Effects in Binaries of Various Periods", The Astrophysical Journal, 616 (1): 562–566, Bibcode:2004ApJ...616..562A, doi:10.1086/423795. 
  12. ^ van Belle, Gerard T., Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, Bibcode:2012A&ARv..20...51V, arXiv:1204.2572Freely accessible, doi:10.1007/s00159-012-0051-2.