Canadian astronomers announced today the first evidence of a magnetic field on a
planet outside of our solar system which is also the first observation of a
planet heating its star. The report was presented this morning by Ph.D.
candidate Evgenya Shkolnik, Dr. Gordon Walker, both of the University of British
Columbia, Vancouver, BC and Dr. David Bohlender of the National Research Council
of Canada / Herzberg Institute for Astrophysics, Victoria, BC at the meeting of
the American Astronomical Society in Atlanta, Georgia. The result may offer
clues about the structure and formation of the giant planet.

The trio observed the sun-like star HD179949 with the 3.6-meter (142-in)
Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii (a 14,000-ft. dormant
volcano) using its high-resolution spectrograph called Gecko. HD179949 is 90
light years away in the direction of the southern constellation of Sagittarius
(the Archer) but it is too faint to be seen without a telescope. It was first
reported to have a close-in planet by Tinney, Butler, Marcy and others in the
first results of the Anglo-Australian planet search in 2000. The planet is at
least 270 times more massive than the Earth, almost as big as Jupiter, and
orbits the star every 3.093 days at 350,000 mph. Such tightly orbiting
"roasters" or "hot jupiters" make up 20% of all known extrasolar planets.

The star’s chromosphere, a thin, hot layer just above the visible photosphere,
was observed in the ultraviolet light emitted by singly-ionized Calcium atoms.
Giant magnetic storms produce hot spots which are visible as bright patches in
this light. Such a persistent hotspot is observed on HD 179949 keeping pace with
the planet in its 3-day orbit for more than a year (or 100 orbits)! The hotspot
appears to be moving across the surface of the star slightly ahead of, but
keeping pace with the planet. Most evidence suggests the star is rotating too
slowly to carry the spot around so quickly.

The best explanation for this traveling hot spot is an interaction between the
planet’s magnetic field and the star’s chromosphere, something predicted by
Steve Saar of the Center for Astrophysics and Manfred Cuntz of the University of
Texas at Arlington in 2000. If so, this is the first ever glimpse of a magnetic
field on a planet outside of our solar system, and may provide clues about the
planet’s structure and formation.

"If we are indeed witnessing the entanglement of the magnetic field of a star
with that of its planet it gives us an entirely new insight into the nature of
closely bound planets." — Dr. Gordon Walker

Obviously, more observations are needed to test if the magnetic interaction is a
transient event or something longer lasting. Also, observations from the 8-meter
Gemini-South Telescope in Chile of this stellar system are underway in the
infrared light emitted by Helium which would map hotspots at higher levels of
the chromosphere.

This work was supported by the Canadian Natural Science and Engineering Research
Council and the National Research Council of Canada.

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Shane Erno’s conception of the flare.