Tau Draconis

Tau Draconis, Latinized from τ Draconis, is an astrometric binary[9] star system in the northern circumpolar constellation of Draco. The star is faintly visible to the naked eye, having an apparent visual magnitude of 4.45.[2] Based upon an annual parallax shift of 22.28 mas as measured from Earth,[1] it is located around 146 light years from the Sun. Its proper motion is propelling it across the sky at the rate of 0.176 arc seconds per year.[10]

Tau Draconis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Draco
Right ascension 19h 15m 33.05868s[1]
Declination +73° 21′ 19.6769″[1]
Apparent magnitude (V) 4.45[2]
Characteristics
Spectral type K2 III:[3]
U−B color index +1.45[2]
B−V color index +1.25[2]
Astrometry
Radial velocity (Rv)−33.70[3] km/s
Proper motion (μ) RA: −115.29[1] mas/yr
Dec.: +103.23[1] mas/yr
Parallax (π)22.28 ± 0.50[1] mas
Distance146 ± 3 ly
(45 ± 1 pc)
Absolute magnitude (MV)+1.19[4]
Details
Mass1.25[3] M☉
Luminosity48[3] L☉
Surface gravity (log g)2.00[5] cgs
Temperature4,413±77[3] K
Metallicity [Fe/H]0.17±0.06[6] dex
Rotational velocity (v sin i)8[7] km/s
Age6.48[3] Gyr
Other designations
τ Dra, 60 Dra, BD+73° 857, FK5 729, HD 181984, HIP 94648, HR 7352, SAO 9366[8]
Database references
SIMBADdata

This is a K-type giant star with a stellar classification of K2 III:,[3] where the semi-colon indicates some uncertainty about its spectral value. It is considered metal-rich[6] star and is past the first dredge-up phase of its post-main sequence evolution, although it shows under-abundances of carbon and oxygen in its spectrum.[5] The star has 1.25[3] times the mass of the Sun and is an estimated 6.48[3] billion years old. It is radiating 48[3] times the solar luminosity from its enlarged photosphere at an effective temperature of 4,413 K.[3]

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. Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, 88.
  4. 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.
  5. Mishenina, T. V.; et al. (October 1995), "Chemical composition of five giants with positive CN-indices.", Astronomy and Astrophysics Supplement, 113: 333, Bibcode:1995A&AS..113..333M.
  6. Taylor, B. J. (February 2002), "A statistical search for supermetallicity in F, G and K stars", Monthly Notices of the Royal Astronomical Society, 329 (4): 839–847, Bibcode:2002MNRAS.329..839T, doi:10.1046/j.1365-8711.2002.05046.x.
  7. Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1), Bibcode:1970CoAsi.239....1B.
  8. "tau Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-05-30.
  9. 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.
  10. Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854.
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