Tau Boötis

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Template: Infobox double star / Maintenance / single coordinate

Tau Bootis ( τ Boo / τ Bootis ) is a double star, the ( 50.9 light years) is located at a distance of about 15.6 parsecs in the southwest of the constellation Bootes. The system consists of the significantly lighter Tau Bootis A, which is a yellowish main sequence star of spectral type F6 IV with an apparent magnitude of 4.50, and thus clearly be seen with the naked eye, as well as from the invisible to the naked eye Tau Bootis B, a red dwarf with the apparent brightness of 11.00, the Tau Bootis a at a distance of 224 AU in 2,000 years on a highly eccentric orbit (0.91 ) orbits, which is also inclined to the observer on Earth to 50.69 °. To Tau Bootis A also revolves on a very narrow path a planet, Tau Bootis A b, which has approximately 4 times Jupiter's mass to the hot Jupiters.

The star

Tau Bootis A

Tau Bootis A has a mass of 1.3 solar masses and has an absolute magnitude of 3.53, a luminosity that is about three times as large as that of our sun. Its diameter is also likely to be slightly higher than that of the sun, for Tau Bootis A, with an age of less than 2 billion years, significantly younger. It contains twice as high proportion of heavy elements like the sun and has a surface temperature of about 6,300 K. The overall life as a main sequence star is 6 billion years, significantly lower than that of the sun.

In 1996, a planetary companion was discovered ( see below). The rotation period of Tau Bootis corresponds to the orbital period of the planet (3.3 days), so that here a rare case of bound rotation is present, in which the planet 's star imposes by appropriate tidal forces the rotation period. The star has a magnetic field that interacts in complex ways with the nearby planet.

Tau Bootis B

Tau Bootis B, due to its low luminosity can be seen only with powerful telescopes. The red dwarf has an absolute magnitude of 10.03, a mass of only about one-third of the Sun's mass and radius, which corresponds to around 60 % of the solar radius; Tau Bootis B belongs to the spectral class M2 V.

The exoplanet

Main article: Tau Bootis b

Tau Bootis b, or Tau Bootis As was discovered by the team of Michel Mayor by measuring the radial velocity of the central star in 1996 and was one of the first discoveries of exoplanets in general. Since the orbital period is virtually identical to the rotation period of Bootis A, first there was doubt whether the test results were actually to be interpreted as the gravitational effect of a planet or whether it was not rather a pulsation phenomenon of the star itself. In 1999, the team of A. Cameron said it had first observed at Tau Bootis From the reflected light from a planet of the central star, but could not confirm the measurement. The planet has a minimum mass of 3.9 Jupiter masses and orbits its star every 3 days, 7 hours and 32 minutes at a distance of about 7 million miles on a nearly circular orbit, resulting in an average train speed of 151 km / s, yields which is more than three times the Mercury.