Tau2 Aquarii

Tau2 Aquarii (τ2 Aqr, τ2 Aquarii) is the Bayer designation for a star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of +4.0.[2] Because the star lies near the ecliptic it is subject to occultations by the Moon.[8]

For other stars with this Bayer designation, see τ Aquarii.
τ2 Aquarii
Location of τ2 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension  22h 49m 35.50157s[1]
Declination –13° 35′ 33.4767″[1]
Apparent magnitude (V) +4.042[2]
Characteristics
Spectral type K5 III[3]
U−B color index +1.948[2]
B−V color index +1.566[2]
Astrometry
Radial velocity (Rv)+1.0[4] km/s
Proper motion (μ) RA: –13.71[1] mas/yr
Dec.: –39.03[1] mas/yr
Parallax (π)10.27 ± 0.29[1] mas
Distance318 ± 9 ly
(97 ± 3 pc)
Absolute magnitude (MV)−1.28[5]
Details
Radius53[6] R☉
Other designations
τ2 Aquarii, 71 Aquarii, BD–14° 6354, FK5 861, HD 216032, HIP 112716, HR 8679, NSV 14329, SAO 165321.[7]
Database references
SIMBADdata

This is an orange-hued[9] giant star with a stellar classification of K5 III.[3] The measured angular diameter, after correction for limb darkening, is 5.12 ± 0.05 mas.[10] At an estimated distance of 318 light-years (97 parsecs) based on parallax measurements,[1] this yields a physical size of about 53 times the radius of the Sun.[6]

References
  1. 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. Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publ. Dept. Astron. Univ. Chile, Publicaciones Universidad de Chile, Department de Astronomy, 1: 1–17, Bibcode:1966PDAUC...1....1G.
  3. Houk, Nancy (1978), "Michigan catalogue of two-dimensional spectral types for the HD stars", Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Ann Arbor: Dept. of Astronomy, University of Michigan, 4, Bibcode:1988mcts.book.....H.
  4. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W.
  5. Pace, G.; Pasquini, L.; Ortolani, S. (2003). "The Wilson-Bappu effect: A tool to determine stellar distances". Astronomy and Astrophysics. 401 (3): 997. arXiv:astro-ph/0301637. Bibcode:2003A&A...401..997P. doi:10.1051/0004-6361:20030163.
  6. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  7. "tau Aqr -- Star in double system", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-08
  8. White, Nathaniel M.; Feierman, Barry H. (September 1987), "A Catalog of Stellar Angular Diameters Measured by Lunar Occultation", Astronomical Journal, 94: 751, Bibcode:1987AJ.....94..751W, doi:10.1086/114513.
  9. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  10. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
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