Epsilon Arietis

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ε Arietis
Aries constellation map.svg
Red circle.svg
Location of ε Arietis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 02h 59m 12.72536s[1]
Declination +21° 20′ 25.5575″[1]
Apparent magnitude (V) 4.63[2] (5.2/5.5)[3]
Spectral type A2 Vs + A2 Vs[4]
U−B color index +0.08[2]
B−V color index +0.04[2]
R−I color index 0.02
Radial velocity (Rv)+0.9 ± 0.9[5] km/s
Proper motion (μ) RA: -13.74[1] mas/yr
Dec.: -5.12[1] mas/yr
Parallax (π)9.81 ± 0.79[1] mas
Distance330 ± 30 ly
(102 ± 8 pc)
ε Ari A
Rotational velocity (v sin i)60[4] km/s
ε Ari B
Rotational velocity (v sin i)60[4] km/s
Other designations
48 Arietis, ADS 2257, BD+20 484, HIP 13914.[6]
ε Ari A: HD 18520, HR 888, SAO 75673.
ε Ari B: HD 18519, HR 887.
Database references
ε Ari A
ε Ari B

Epsilon Arietis (ε Ari, ε Arietis) is the Bayer designation for a visual binary[7] star system in the northern constellation of Aries. It has a combined apparent visual magnitude of 4.63[2] and can be seen with the naked eye, although the two components are too close together to be resolved without a telescope. With an annual parallax shift of 9.81 mas,[1] the distance to this system can be estimated as 330 light-years (100 parsecs), give or take a 30 light-year margin of error.

The brighter member of this pair has an apparent magnitude of 5.2.[3] At an angular separation of 1.426 ± 0.010 arcseconds from the brighter component, along a position angle of 209.2° ± 0.3°,[7] is the magnitude 5.5 companion.[3] Both are A-type main sequence stars with a stellar classification of A2 Vs.[4] (The 's' suffix indicates that the absorption lines in the spectrum are distinctly narrow.) In the 2009 Catalogue of Ap, HgMn and Am stars, the two stars have a classification of A3 Ti,[3] indicating they are Ap stars with an anomalous abundance of titanium. Within the measurement margin of error, their projected rotational velocities are deemed identical at 60 km/s.[4]


This star system, along with δ Ari, ζ Ari, π Ari, and ρ3 Ari, were Al Bīrūnī's Al Buṭain (ألبطين), the dual of Al Baṭn, the Belly.[8] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Buṭain were the title for five stars :δ Ari as Botein, π Ari as Al Buṭain I, ρ3 Ari as Al Buṭain II, ε Ari as Al Buṭain III and ζ Ari as Al Buṭain IV[9]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Eggen, Olin J. (November 1963), "Luminosities, colors, and motions of the brightest A-type stars", Astronomical Journal, 68: 697, Bibcode:1963AJ.....68..697E, doi:10.1086/109198.
  3. ^ a b c d Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars" (PDF), Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788.
  4. ^ a b c d e Royer, F.; et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943.
  5. ^ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  6. ^ "eps Ari". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-08-05.
  7. ^ a b Scardia, M.; Prieur, J.-L.; Pansecchi, L.; Argyle, R. W.; Basso, S.; Sala, M.; Ghigo, M.; Koechlin, L.; Aristidi, E. (January 2007), "Speckle observations with PISCO in Merate - III. Astrometric measurements of visual binaries in 2005 and scale calibration with a grating mask", Monthly Notices of the Royal Astronomical Society, 374 (3): 965–978, Bibcode:2007MNRAS.374..965S, doi:10.1111/j.1365-2966.2006.11206.x.
  8. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 83. ISBN 0-486-21079-0. Retrieved 2010-12-12.
  9. ^ Jack W. Rhoads - Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971

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