Observational Evidence for a Non Solar-Type Dynamo Operating in Late-Type Stars

We present high-resolution images of the young rapidly rotating GO dwarf HD 171488 using both Stokes I and Stokes V data taken over four epochs. Using the good phase coverage of our data we measure differential rotation for each epoch. The results show the highest measurements of differential rotation ever measured using Zeeman-Doppler imaging techniques. We also find that the differential rotation measurement obtained from Stokes V data is approximately the same as that derived from the Stokes I data and that they show no temporal evolution. Other measurements of differential rotation using both brightness and magnetic data have been made for the K1 V AB Dor where there is a large variation between the two data sets. For AB Dor this indicates that magnetic regions are not anchored at the same depth in the convective zone, and therefore do not experience the same shear. The marginal difference in the differential rotation measurements for Stokes I and V data and the absense of any temporal evolution for HD 171488 further supports the existence of a non solar-type dynamo, as HD 171488 has a much thinner convective zone than AB Dor.