Cool Stars 14 - Submitted Abstract # 269
This version created on 05 October 2006

Extreme Levels of Surface Differential Rotation on the young G0 
dwarf HD 171488

S.V. Jeffers, LATT, Observatoire Midi-Pyrenees, Toulouse, France
J.-F. Donati, LATT, Observatoire Midi-Pyrenees, Toulouse, France

We present high-resolution images of the young rapidly rotating GO
dwarf HD 171488 using both Stokes I and Stokes V data.  The
observations were secured with the MUSICOS spectropolarimeter at
Telescope Bernard Lyot from 31 May to 10 June 2005.  The photospheric
surface brightness distributions show a strong and slightly decentered
polar cap that dominates over weak high and low latitude spot
features.  The large-scale magnetic field topology shows a strong ring
of anti-clockwise azimuthal field with a latitudinal dependence on
polarity and large negative regions of radial polarity at all
latitudes.  The excellent phase coverage of our data set allowed the
tracking of starspots with time to obtain the highest measurement of
surface differential rotation using Zeeman-Doppler imaging techniques.
We measure that the equator laps the pole every 15 days, for brighness
data and 8 days for magnetic data, which is significantly higher than
previous measurements of other late-type rapid rotators.  We find that
the differential rotation measurement using the Stokes V data is
approximately twice that of measured using Stokes I data.

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