Tau Boötis


Tau Boötis, Latinized from 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.

Stellar components

The system is a binary. The primary component is a yellow-white dwarf and secondary is a dim red dwarf. 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. The magnetic activity cycle for this star shows a period of 122 days − much shorter than the solar cycle.
Tau Boötis B is a dim red dwarf orbiting the primary star at a distance of 240 AU. One orbit around the primary would take approximately one thousand years to complete.

Planetary system

In 1996 the planet Tau Boötis b was discovered orbiting the primary star by a team of astronomers led by R. Paul Butler. There are also some indications of another planet orbiting the star with a period of roughly 5000 days; however, this could be due to an instrumental effect or a stellar magnetic activity cycle. In an unusual case of role-reversal, it appears that Tau Boötis's rotation has been tidally locked to Tau Boötis b.
The planet and its host star was one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star. The process involved public nomination and voting for the new names, and the IAU announced the new names in mid-December 2015. However, the IAU annulled the vote for the system, as the winning names were judged not to conform with the IAU rules for naming exoplanets. The names garnered the majority of the votes cast for the system, and also making up a significant proportion of all votes cast as part of the contest.