Morphologies of the Nebulae around "born-again" Central Stars of   Planetary Nebulae
  While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In the case of those objects that underwent a very late helium flash (called VLTP objects or ``born-again'' PNe) it seems to be different. The first, hydrogen-rich PN, is more or less round. The ejecta from the VLTP event, in contrast, are extremely asymmetrical. 
S. Kimeswenger (1), A.A. Zijlstra (2), P.A.M. van Hoof (3), M. Hajduk   (4), F. Herwig (5), M.F.M. Lechner (1), S.P.S. Eyres...