Tau Boötis

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Tau Boötis
Diagram showing star positions and boundaries of the Eridanus constellation and its surroundings
Cercle rouge 100%.svg

A star chart of the constellation of Boötes showing the position of Tau Boötis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Boötes
Right ascension 13h 47m 15.74s[1]
Declination +17° 27′ 24.9″[1]
Apparent magnitude (V) 4.50[2]
Spectral type F6 IV[2]
U−B color index 0.04
B−V color index 0.48[2]
R−I color index 0.24
Variable type Variable star
Radial velocity (Rv) -15.6 km/s
Proper motion (μ) RA: -479.53 ± 0.16[1] mas/yr
Dec.: 53.49 ± 0.13[1] mas/yr
Parallax (π) 64.03 ± 0.19[1] mas
Distance 50.9 ± 0.2 ly
(15.62 ± 0.05 pc)
Absolute magnitude (MV) 3.53
Mass 1.3 / 0.4 M
Radius 1.331 ± 0,027 R
Luminosity 3.0[2] L
Surface gravity (log g) 4.30[2] cgs
Temperature 6,360[3] K
Metallicity 210%[citation needed]
Rotation 3.31 days[3]
Rotational velocity (v sin i) 14 km/s
Age 1.6–2.3 [4] Gyr
Other designations
4 Boötis, ADS 9025, BD+18°2782, CCDM 13473+1727, FK5 507, GC 18637, GCTP 3144.00, GJ 527, HD 120136, HIP 67275, HR 5185, LTT 14021, SAO 100706
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)
Database references

Tau Boötis (τ Boo, τ Boötis) is an F-type main-sequence star approximately 51 light-years away[1] in the constellation of Boötes. The system is also a binary star system, with the secondary star being a red dwarf. As of 1999, an extrasolar planet has been confirmed to be orbiting the primary star.

Stellar components[edit]

The system is a binary. The primary component is a yellow-white dwarf (spectral type F7 V) and secondary is a dim red dwarf (spectral type M2 V). The system is relatively nearby, distance being about 51 light years. The primary star should be easily visible to the unaided eye under dark skies.

The primary star, Tau Boötis A is a yellow-white dwarf. It is 20% more massive than our Sun and thus is somewhat brighter and hotter. It has a radius 1.9 times solar, and is probably about 1.3 billion years old. Since it is more massive than the Sun, its lifespan is shorter - less than 6 billion years. Tau Bootis is the first star apart from the sun to be observed changing the polarity of its magnetic field.[5] It is also listed as a suspected variable star.

Tau Boötis B (with a capital B, as opposed to the planet) is a dim red dwarf orbiting the primary star at a distance of 240 AU. One orbit around the primary would take thousands of years to complete.

Planetary system[edit]

In 1996 a planet, designated as Tau Boötis b, was discovered orbiting the primary star.[6] There are also some indications of another, more distant, planet orbiting the star. In an unusual case of role-reversal, it appears that Tau Boötis' rotation has been tidally locked to Tau Boötis b.[7] The planet was discovered by a team of astronomers led by Geoff Marcy and R. Paul Butler.[6]

The Tau Boötis A planetary system[8]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 6±0.28 MJ 0.0481 ± 0.028 3.312463 ± 0.000014 0.023 ± 0.015 44.5 ± 1.5°


  1. ^ a b c d e f 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.  Vizier catalog entry
  2. ^ a b c d e Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics 352: 495–507, Bibcode:1999A&A...352..495M 
  3. ^ a b Strassmeier, Klaus G. (September 2009), "Starspots", The Astronomy and Astrophysics Review 17 (3): 251–308, Bibcode:2009A&ARv..17..251S, doi:10.1007/s00159-009-0020-6 
  4. ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal 687 (2): 1264–1293. arXiv:0807.1686. Bibcode:2008ApJ...687.1264M. doi:10.1086/591785. 
  5. ^ Donati, J.-F. et al. (2008). "Magnetic cycles of the planet-hosting star Tau Boötis". Monthly Notices of the Royal Astronomical Society 385 (3): 1179–1185. arXiv:0802.1584. Bibcode:2008MNRAS.385.1179D. doi:10.1111/j.1365-2966.2008.12946.x. 
  6. ^ a b Butler, R. Paul et al. (1997). "Three New 51 Pegasi Type Planets". The Astrophysical Journal Letters 474 (2): L115–L118. Bibcode:1997ApJ...474L.115B. doi:10.1086/310444. 
  7. ^ Walker, G. A. H. et al. (2008). "MOST detects variability on tau Bootis possibly induced by its planetary companion". Astronomy and Astrophysics 482 (2): 691–697. arXiv:0802.2732. Bibcode:2008A&A...482..691W. doi:10.1051/0004-6361:20078952. 
  8. ^ Butler, R. P. et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701. 

External links[edit]

Coordinates: Sky map 13h 47m 15.7s, +17° 27′ 25″