Star and planet tie the knot

University of Hawaiʻi at Mānoa
Posted: Dec 6, 2006

Astronomers using the Canada-France-Hawaii telescope on Mauna Kea have announced the discovery of magnetism in a star 50 light-years away. The magnetic field is 100 times weaker than that of a typical refrigerator magnet.

The star, called Tau Bootis, is rather like the sun, except that it is orbited every three days by an enormous planet that is over 1000 times as massive as Earth.

"The star's magnetic field is tied up in knots, possibly because of the influence of its close-in giant planet," said University of Hawaii astronomer Evgenya Shkolnik. "We are all used to the idea of a star influencing conditions on a planet, but it is truly amazing to discover the extent to which planets can influence their stars, in a kind of celestial role reversal."

Shkolnik is a member of an international team led by two French astronomers, Claude Catala of the Observatoire de Paris and Jean-François Donati of Observatoire Midi-Pyrénées. They made the discovery using an extremely sensitive high-resolution spectropolarimeter on the Canada-France-Hawaii Telescope on Mauna Kea.

This is the only system known where the planet and star are tidally locked so that one side of the star always sees the same side of the planet. The star and planet both make one rotation, and one orbit, in about 3 days. However, the star's equator is rotating about 20 percent faster than its pole.

Indirect evidence of planet-induced stellar magnetic activity was first reported by team members Shkolnik, David Bohlender (National Research Council of Canada/Herzberg Institute of Astrophysics) and their colleagues in 2005 for two similar stars.

New data scheduled to be collected next spring will map the surface of the star in more detail, contributing additional information to the studies of star-planet interactions.

This discovery is published in a Letter to the journal Monthly Notices of Royal Astronomical Society.

The Paper:

"The magnetic field of the planet-hosting star tau Bootis"
C. Catala, J.-F. Donati, E. Shkolnik, D. Bohlender, E. Alecian

CFHT press release:

The Institute for Astronomy at the University of Hawaii conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of Schools and Colleges, the University of Hawaii is the state's sole public system of higher education. The UH System provides an array of undergraduate, graduate, and professional degrees and community programs on 10 campuses and through educational, training, and research centers across the state. UH enrolls more than 50,000 students from Hawaii, the U.S. mainland, and around the world.

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