Kimeswenger, S. ; Zijlstra, A. A. ; van Hoof, P. A. M. ; Hajduk, M. ; Herwig, F. ; Lechner, M. F. M. ; Eyres, S. P. S. ; van de Steene, G. C.

published in Hydrogen-Deficient Stars, 391, pp. 177 (2008)

Abstract: 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.

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