Epsilon Tucanae

Epsilon Tucanae (ε Tuc, ε Tucanae) is a solitary[8] star in the southern constellation of Tucana. With an apparent visual magnitude of +4.50,[2] it is faintly visible to the naked eye. Based upon an annual parallax shift of 8.74 mas as seen from Earth, it is located around 373 light years from the Sun.

Epsilon Tucanae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Tucana
Right ascension 23h 59m 54.97761s[1]
Declination −65° 34′ 37.6804″[1]
Apparent magnitude (V) +4.50[2]
Characteristics
Spectral type B8 V[3] or B9 IV[4]
U−B color index −0.28[2]
B−V color index −0.08[2]
Astrometry
Radial velocity (Rv)+8.8±2.8[5] km/s
Proper motion (μ) RA: +47.93[1] mas/yr
Dec.: −22.95[1] mas/yr
Parallax (π)8.74 ± 0.18[1] mas
Distance373 ± 8 ly
(114 ± 2 pc)
Absolute magnitude (MV)−0.80[6]
Details[3]
Mass4.00±0.20 M☉
Luminosity389 L☉
Surface gravity (log g)3.9±0.1 cgs
Temperature13,000±500 K
Rotational velocity (v sin i)300±20 km/s
Age123 Myr
Other designations
ε Tuc, CPD−66° 3819, FK5 903, HD 224686, HIP 118322, HR 9076, SAO 255619[7]
Database references
SIMBADdata

Levenhagen and Leister (2008) classified this star as B8 V,[3] indicating a blue-white hued B-type main sequence star. However, Hiltner, Garrison, and Schild (1969) listed it with a classification of B9 IV,[4] suggesting it may be a more evolved subgiant star. It is a rapidly rotating Be star that is an estimated 78% of the way through its main sequence lifetime.[9] The projected rotational velocity is 300 km/s,[3] which is giving it an oblate shape with an equatorial bulge that is an estimated 36% larger than the polar radius.[10] It has a weak magnetic field with a strength of 74±24 G.[11]

It is the last star in the Hipparcos catalogue, HIP 118322, from the Hipparcos (1989–1993) astrometry satellite.

References
  1. van Leeuwen, F. (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. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
  3. Levenhagen, R. S.; Leister, N. V. (2006), "Spectroscopic Analysis of Southern B and Be Stars", Monthly Notices of the Royal Astronomical Society, 371: 252–62, arXiv:astro-ph/0606149, Bibcode:2006MNRAS.371..252L, doi:10.1111/j.1365-2966.2006.10655.x.
  4. Hiltner, W. A.; et al. (July 1969), "MK Spectral Types for Bright Southern OB Stars", Astrophysical Journal, 157: 313, Bibcode:1969ApJ...157..313H, doi:10.1086/150069.
  5. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  6. 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.
  7. "eps Tuc -- Be Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-04-22.
  8. 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.
  9. Zorec, J.; et al. (October 2005), "On the evolutionary status of Be stars. I. Field Be stars near the Sun", Astronomy and Astrophysics, 441 (1): 235–248, arXiv:astro-ph/0509119, Bibcode:2005A&A...441..235Z, doi:10.1051/0004-6361:20053051.
  10. Belle, G. T. (2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20: 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.
  11. Hubrig, S.; et al. (July 2009), "Magnetic survey of emission line B-type stars with FORS 1 at the VLT", Astronomische Nachrichten, 330 (7): 708, arXiv:0907.0882, Bibcode:2009AN....330..708H, doi:10.1002/asna.200911236.
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