On the excitation of PG1159-type pulsations
  Stability properties are presented of dipole and quadrupole nonradial oscillation modes of model stars that experienced a late helium shell flash on their way to the white-dwarf cooling domain. The computed instability domains are compared with the observed hot variable central stars of planetary nebulae and the GW Vir pulsators. 
A. Gautschy, L.G. Althaus, H. Saio