The closure of the set of periodic modules over a concealed canonical   algebra is regular in codimension one
  Let A be a concealed canonical algebra and d the dimension vector of an A-module which is periodic respect to the action of the Auslander-Reiten translation In the paper, we investigate the union of the closures of the orbits of the periodic A-modules of dimension vector d. We show that this set is closed and regular in codimension one. 
Grzegorz Bobinski, Grzegorz Zwara
math.RT