High levels of surface differential rotation on the young G0 dwarf HD171488

International audienceWe present high-resolution images of the young, rapidly rotating G0 dwarf HD171488, using both Stokes I and Stokes V data. The observations were secured with the MuSiCoS spectropolarimeter at Telescope Bernard Lyot from 2005 May 31 to June 10. The photospheric surface brightness distributions show a strong and slightly decentred polar cap that dominates over weak high- and low-latitude spot features. The large-scale magnetic field topology shows a strong ring of anticlockwise azimuthal field with a latitudinal dependence on polarity and large regions of radial field with negative polarity at all latitudes. Using the good phase coverage of our data, we measure the differential rotation on HD171488. The results indicate that the equator laps the pole every 12 days for brightness data and 13 days for magnetic data, which is the highest measurement of differential rotation obtained using Zeeman-Doppler imaging techniques. Spectropolarimetric observations were obtained, from 2005 May 31 to June 10, with the MuSiCoS echelle spectropolarimeter at the Telescope Bernard Lyot (Observatoire du Pic du Midi, France). E-mail: s.v.jeffers@uu.n