Tau2 Aquarii

For other star systems with this Bayer designation, see Tau Aquarii.

τ² Aquarii

Location of τ^2 Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius
Right ascension	22^h 49^m 35.50157^s[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
Distance	318 ± 9 ly (97 ± 3 pc)
Absolute magnitude (MV)	−1.28[5]
Details
Radius	53[6] R☉
Other designations
Tau Aquarii, 71 Aquarii, BD–14 6354, FK5 861, HD 216032, HIP 112716, HR 8679, NSV 14329, SAO 165321.[7]

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] This is an orange-hued^[8] 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.^[9] 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:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(97\cdot 5.12\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 107\cdot R_{\bigodot }\end{aligned}}}$

7. "tau Aqr -- Star in double system", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-08
8. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
9. 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

External links

• Image τ² Aquarii