SEARCH FOR ROTATION IN WHITE-DWARFS

We report high-resolution spectroscopic observations of the NLTE H alp ha core in 28 DA white dwarfs. From a comparison with theoretically br oadened NLTE models projected rotation velocities can be determined. T he majority of objects are found to be compatible with zero or very sm all rotation with typical upper limits for v sin i of 15 km/s, corresp onding to periods of hours or longer. The implications for the loss of angular momentum during the evolution of the progenitors is discussed . Three new magnetic white dwarfs are detected with very small tangent ial fields in the range of 30 to 50 kG. In two more magnetic objects k nown before we found field strengths significantly larger than the mea n longitudinal fields determined from the circular polarization. Very puzzling is the result for three ZZ Ceti stars in the sample, which al l seem to have projected rotational velocities between 30 and 45 km/s, in conflict with asteroseismological results.