Canada-France-Hawaii Telescope (CFHT), one of the oldest facilities on the summit of Mauna-Kea, is at the forefront of optical astronomy through stunning wide field images of the universe, thanks to MegaPrime, the largest digital camera in operation on a telescope.

However, for the past months, a new instrument nick-named ESPaDOnS has shared the telescope with MegaPrime to look at stars in a search of their magnetic field. As shown with the publication today in the journal Nature of the first detection of the magnetic field inside a growing star's dusty disk, this new instrument is now offering a unique opportunity to study stars through the observation of their magnetic activity.

Jean-Francois Donati, who led the construction of ESPaDOnS before its delivery to CFHT, and his colleagues used the instrument to study visible light coming from the FU Orionis system, which contains a young star that is being fed by a surrounding disk. The magnetic field inside this disk helps to slow its rotation, causing material to fall towards the central star. Although theoretical models predict this crucial role, the magnetic field close to the star has not hitherto been directly measured.

Light from FU Orionis is rotated, or polarized, by magnetic fields in the disk. By measuring this polarization, the astronomers found that the magnetic field slows down the disk material much more than models predict. This may explain why the star does not spray out some of the infalling material as a jet, a feature seen in other star-disk systems.
Contact in France: Jean-Francois Donati (Observatoire Midi-Pyrenees, Toulouse, France) Tel: +33 561 332 917

Contact at CFHT: Christian Veillet - 1 (808) 885 2143 or 1 (808) 938 3905