Rotation velocities of white dwarfs determined from the CaII K line
  We determine projected rotation velocities v sini in DAZ white dwarfs, for the first time using the rotational broadening of the CaII K line. The results confirm previous findings that white dwarfs are very slow rotators, and set even more stringent upper limits of typically less than 10 km/s. The few exceptions include 3 stars known or suspected to be variable ZZ Ceti stars, where the line broadening is very likely not due to rotation. The results demonstrate that the angular momentum of the core cannot be preserved completely between main sequence and final stage. 
L. Berger, D. Koester, R. Napiwotzki, I. N. Reid, B. Zuckerman