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21 Arietis (abbreviated 21 Ari) is a binary star system in the northern constellation of Aries. 21 Arietis is the Flamsteed designation. It has a combined apparent visual magnitude is 5.57; the brighter member is magnitude 6.40 while the fainter star is magnitude 6.48. The distance to this star system, based upon an annual parallax shift of 19.58 mas, is 167 light-years (51 parsecs). The pair orbit each other with a period of 23.70 years and an eccentricity of 0.68.

The system was initially thought to be a triple system in 1981, since the orbit of the system predicted a mass greater than would be expected from its F6V spectral type. This was later rejected because the distance to the system was overestimated. However, while observing the spectrum of the system, it was found that a giant planet may be causing radial velocity variations. The purported planet would have a mass of 1.40 ± 0.36 M_J, an orbital period of 925 days and orbit the primary star.

References

1. ^ 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, S2CID 18759600.
2. ^ Holmberg, J.; Nordström, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191, S2CID 118577511.
3. ^ 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:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
4. Harlan, E. A. (September 1969), "MK classifications for F- and G-type stars. I", Astronomical Journal, 74: 916–919, Bibcode:1969AJ.....74..916H, doi:10.1086/110881.
5. ^ "* 21 Ari". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-18.
6. Hartkopf, William I.; Mason, Brian D.; McAlister, Harold A. (January 1996), "Binary Star Orbits From Speckle Interferometry. VIII. Orbits of 37 Close Visual System", Astronomical Journal, 111: 370, Bibcode:1996AJ....111..370H, doi:10.1086/117790.
7. ^ Muterspaugh, Matthew W.; Lane, Benjamin F.; Kulkarni, S. R.; Konacki, Maciej; Burke, Bernard F.; Colavita, M. M.; Shao, M.; Hartkopf, William I.; Boss, Alan P.; Williamson, M. (2010). "The Phases Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems". The Astronomical Journal. 140 (6): 1657. arXiv:1010.4048. Bibcode:2010AJ....140.1657M. doi:10.1088/0004-6256/140/6/1657. S2CID 59585356.
8. ^ Balachandran, Suchitra (May 1, 1990), "Lithium depletion and rotation in main-sequence stars", Astrophysical Journal, Part 1, 354: 310–332, Bibcode:1990ApJ...354..310B, doi:10.1086/168691.
9. Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
10. Couteau, P.; Morel, P. J. (1982). "Is 21 Ari = Cou 79 a multiple system?". Astronomy and Astrophysics. 105: 323. Bibcode:1982A&A...105..323C.

External links

• HR 657
• CCDM J02157+2503
• Image 21 Arietis

v t e Constellation of Aries
Aries in Chinese astronomy List of stars in Aries
Stars	Bayer α (Hamal) β (Sheratan) γ (Mesarthim) δ (Botein) ε ζ η θ ι κ λ μ ν ξ ο π ρ ρ ρ σ τ τ Flamsteed 1 4 7 10 11 14 15 16 19 20 21 23 26 27 29 30 31 33 35 36 38 39 (Lilii Borea) 40 41 (Bharani) 47 49 50 51 52 53 54 55 56 59 60 62 64 65 66 54 Cet 85 Cet Variable TZ UX VZ (16 Tri) HR 577 728 803 952 999 HD 12661 20367 Other BD+20°307 HIP 14810 HAT-P-25 Teegarden's Star WASP-11/HAT-P-10 WD 0145+234
Exoplanets α Arietis b HD 12661 b c HIP 14810 b c d Teegarden's Star b c WASP-11b/HAT-P-10b
Galaxies	NGC 677 680 691 694 695 716 765 770 772 781 803 817 820 821 871 877 900 901 903 904 918 935 938 972 990 992 1024 1134 1156 Other 1ES 0229+200 3C 79 4C +28.07 AO 0235+164 IC 167 IC 1801 PSO J0309+27 Segue 2 UGC 2140
Galaxy clusters MS 0302+17
Astronomical events GRB 060218
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