11 Arietis

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11 Arietis
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 02h 06m 49.23558s[1]
Declination +25° 42′ 16.3939″[1]
Apparent magnitude (V) 6.01[2]
Spectral type B9 IV-Vn[3]
U−B color index –0.26[4]
B−V color index –0.04[4]
Radial velocity (Rv) –9[5] km/s
Proper motion (μ) RA: +19.46[1] mas/yr
Dec.: –14.31[1] mas/yr
Parallax (π) 3.72 ± 0.38[1] mas
Distance approx. 880 ly
(approx. 270 pc)
Radius 2.8[6] R
Rotational velocity (v sin i) 249[7] km/s
Other designations
BD+25 349, HD 12885, HIP 9859, HR 615, SAO 75149.[8]

11 Arietis is the Flamsteed designation for a star in the northern constellation of Aries. It has an apparent visual magnitude of 6.01,[2] which makes it a challenging target to view with the naked eye in suitably dark skies. Based upon an annual parallax shift of 3.72 mas,[1] the distance to this star is approximately 880 light-years (270 parsecs).

Eta Aquarii has a stellar classification of B9 IV-Vn,[3] which may indicate that it is beginning to evolve away from the main sequence into a subgiant as the supply of hydrogen at its core becomes exhausted. At present it has an estimated 2.8[6] times the radius of the Sun, but this will increase as it continues to evolve into a giant star. Eta Aquarii is spinning rapidly with a projected rotational velocity of 249 km/s.[7] This motion, combined with the Doppler effect, is causing the absorption lines in the spectrum to spread out and become 'nebulous', as indicated by the 'n' suffix in the classification.


  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 Høg, E.; et al. (March 2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy and Astrophysics 355: L27–L30, Bibcode:2000A&A...355L..27H, doi:10.1888/0333750888/2862. 
  3. ^ a b Cowley, A. (November 1972), "Spectral classification of the bright B8 stars", Astronomical Journal 77: 750–755, Bibcode:1972AJ.....77..750C, doi:10.1086/111348. 
  4. ^ a b Crawford, D. L. (February 1963), "U, b, v, and Hβ Photometry for the Bright B8- and B9-TYPE Stars", Astrophysical Journal 137: 530, Bibcode:1963ApJ...137..530C, doi:10.1086/147526. 
  5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495...... 
  6. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451. 
  7. ^ a b Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224. 
  8. ^ "CCDM J02068+2542AB -- Double or multiple star", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-07-18. 

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