Tau Boötis
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Boötes |
| Right ascension | 13h 47m 15.74s |
| Declination | +17° 27′ 24.9″ |
| Apparent magnitude (V) | 4.50 |
| Characteristics | |
| Spectral type | F6 IV |
| U−B color index | 0.04 |
| B−V color index | 0.48 |
| R−I color index | 0.24 |
| Variable type | Variable star |
| Astrometry | |
| Radial velocity (Rv) | -15.6 km/s |
| Proper motion (μ) |
RA: -479.53 ± 0.16 mas/yr Dec.: 53.49 ± 0.13 mas/yr |
| Parallax (π) | 64.03 ± 0.19mas |
| Distance | 50.9 ± 0.2 ly (15.62 ± 0.05 pc) |
| Absolute magnitude (MV) | 3.38 |
| Details | |
| τ Boo A | |
| Mass | 1.3 M☉ |
| Radius | 1.331 ± 0,027 R☉ |
| Luminosity | 3.0 L☉ |
| Surface gravity (log g) | 4.30 cgs |
| Temperature | 6,360 K |
| Metallicity | 210% |
| Rotation | 3.31 days |
| Rotational velocity (v sin i) | 15.6±1.0 km/s |
| Age | 1.6–2.3 Gyr |
| τ Boo B | |
| Mass | 0.4 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
|
Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.) |
|
| Database references | |
| SIMBAD | data |
Tau Boötis (τ Boo, τ Boötis) is an F-type main-sequence star approximately 51 light-years away 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.
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 percent more massive than the 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. 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.
In 1996 a planet, designated as Tau Boötis b, was discovered orbiting the primary star. 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. The planet was discovered by a team of astronomers led by Geoff Marcy and R. Paul Butler.
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