Tau2 Arietis

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Aries constellation map.svg
Red circle.svg
Location of τ2 Arietis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Aries
Right ascension  03h 22m 45.24006s[1]
Declination +20° 44′ 31.4382″[1]
Apparent magnitude (V) +5.09[2]
Spectral type K3 III[3]
U−B color index +1.27[2]
B−V color index 1.238[4]
Radial velocity (Rv)+2.45 ± 0.24[4] km/s
Proper motion (μ) RA: –51.59[1] mas/yr
Dec.: –16.06[1] mas/yr
Parallax (π)10.27 ± 0.60[1] mas
Distance320 ± 20 ly
(97 ± 6 pc)
Absolute magnitude (MV)+0.17[5]
Radius19[4] R
Luminosity120[4] L
Surface gravity (log g)2.1[4] cgs
Temperature4,406[4] K
Metallicity [Fe/H]+0.02[4] dex
Rotational velocity (v sin i)3.4[4] km/s
Other designations
τ2 Ari, 63 Arietis, BD+20 551, HD 20893, HIP 15737, HR 1015, SAO 75899.[6]
Database references

Tau2 Arietis, Latinized from τ2 Arietis, is the Bayer designation for a binary star[7] in the northern constellation on Aries; the combined apparent visual magnitude of this system is +5.09,[2] which is bright enough to be seen with the naked eye. With an annual parallax shift of 10.27 mas,[1] it is located at a distance of approximately 320 light-years (98 parsecs) from Earth, give or take a 20 light-year margin of error. At this distance the brightness of the star is diminished by 0.18 in magnitude because of extinction from interstellar gas and dust.[8]

The primary component is an evolved giant star with a stellar classification of K3 III,[9] it has expanded to 19 times the radius of the Sun, from which it is radiating 120 times the Sun's luminosity.[4] This energy is being emitted into outer space from the outer atmosphere at an effective temperature of 4,406 K,[4] giving it the cool orange glow of a K-type star. At an angular separation of 0.53 arcseconds is a magnitude 8.50 companion.[7]


  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 Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133: 475, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475.
  3. ^ Cenarro, A. J.; et al. (January 2007), "Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters", Monthly Notices of the Royal Astronomical Society, 374 (2): 664–690, arXiv:astro-ph/0611618, Bibcode:2007MNRAS.374..664C, doi:10.1111/j.1365-2966.2006.11196.x.
  4. ^ a b c d e f g h i j Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  5. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. ^ "63 Ari". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-18.
  7. ^ a b 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.
  8. ^ Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272
  9. ^ Roman, Nancy G. (July 1952), "The Spectra of the Bright Stars of Types F5-K5", Astrophysical Journal, 116: 122, Bibcode:1952ApJ...116..122R, doi:10.1086/145598.

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