Alpha Tucanae

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α Tucanae
Tucana constellation map.svg
Red circle.svg
Location of α Tucanae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Tucana
Right ascension 22h 18m 30.09478s[1]
Declination –60° 15′ 34.5263″[1]
Apparent magnitude (V) 2.86[2]
Spectral type K3 III[3]
U−B color index +1.54[2]
B−V color index +1.39[2]
Radial velocity (Rv)+45.8[4] km/s
Proper motion (μ) RA: −70.72[1] mas/yr
Dec.: −39.44[1] mas/yr
Parallax (π)17.7324 ± 0.3290 mas[5]
Distance184 ± 3 ly
(56 ± 1 pc)
Absolute magnitude (MV)-1.05[6]
Absolute bolometric
Period (P)4197.7 days
Eccentricity (e)0.39
Periastron epoch (T)18666.4
Argument of periastron (ω)
Semi-amplitude (K1)
7.2 km/s
Other designations
CPD−60° 7561, FK5 841, HD 211416, HIP 110130, HR 8502, SAO 255193.[8]
Database references

Alpha Tucanae (α Tuc, α Tucanae) is a binary star system in the southern circumpolar constellation of Tucana. With an apparent visual magnitude of 2.86,[2] it can be seen with the naked eye from the southern hemisphere. Using parallax measurements, the distance to this system can be estimated as 200 light-years (61 parsecs).[1] A cool star with a surface temperature of 4300 K, it is 424 times as luminous as the sun and 37 times its diameter. It is 2.5 to 3 times as massive. It is unclear what stage of evolution the star is in.[9]

This is a spectroscopic binary, which means that the two stars have not been individually resolved using a telescope, but the presence of the companion has been inferred from measuring changes in the spectrum of the primary. The orbital period of the binary system is 4197.7 days (11.5 years).[7] The primary component has a stellar classification of K3 III,[3] which indicates it is a giant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence. It has the characteristic orange hue of a K-type star.


  1. ^ a b c d e 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. ^ a b c d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor: Dept. of Astronomy, University of Michigan,
  4. ^ Buscombe, W.; Kennedy, P. M. (1968), "Stellar radial velocities from coudé spectrograms", Monthly Notices of the Royal Astronomical Society, 139 (3): 341–346, Bibcode:1968MNRAS.139..341B, doi:10.1093/mnras/139.3.341
  5. ^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  6. ^ a b Pasquini, L.; de Medeiros, J. R.; Girardi, L. (2000). "Ca II activity and rotation in F-K evolved stars". Astronomy and Astrophysics. 361: 1011–1022. arXiv:astro-ph/0008109. Bibcode:2000A&A...361.1011P.
  7. ^ a b Pourbaix, D.; et al. (2004), "SB9: The Ninth Catalogue of Spectroscopic Binary Orbits", Astronomy & Astrophysics, 424: 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088
  8. ^ "alf Tuc -- Spectroscopic binary", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-20
  9. ^ Kaler, Jim. "Alpha Tucanae". Stars. University of Illinois. Retrieved 19 October 2013.