Alpha Tucanae

α Tucanae

Location of α Tucanae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Tucana
Right ascension	22^h 18^m 30.11244^s[1]
Declination	−60° 15′ 34.6664″[1]
Apparent magnitude (V)	2.86[2]
Characteristics
Spectral type	K3 III[3]
U−B color index	+1.54[2]
B−V color index	+1.39[2]
Astrometry
Radial velocity (Rv)	+45.8[4] km/s
Proper motion (μ)	RA: −77.000[1] mas/yr Dec.: −32.823[1] mas/yr
Parallax (π)	17.7324 ± 0.3290 mas[1]
Distance	184 ± 3 ly (56 ± 1 pc)
Absolute magnitude (MV)	−1.05[5]
Absolute bolometric magnitude (Mbol)	−1.97[5]
Orbit[6]
Period (P)	4197.7 days
Eccentricity (e)	0.39
Periastron epoch (T)	18666.4
Argument of periastron (ω) (secondary)	48.5°
Semi-amplitude (K1) (primary)	7.2 km/s
Details
Mass	2.5 - 3[7] M☉
Radius	37[7] R☉
Luminosity	424[7] L☉
Temperature	4300[7] K
Other designations
CPD−60°7561, FK5 841, HD 211416, HIP 110130, HR 8502, SAO 255193[8]
Database references
SIMBAD	data

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 184 light-years (56 parsecs). 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.^[7]

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).^[6] 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.

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. 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. Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1975mcts.book.....H
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. 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.
6. 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
7. Kaler, Jim. "Alpha Tucanae". Stars. University of Illinois. Retrieved 19 October 2013.
8. "alf Tuc -- Spectroscopic binary", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-20