A NEW-GENERATION OF PHOTOIONIZATION CODES - 3-DIMENSIONAL MODELS - THE BIPOLAR PLANETARY-NEBULA IC-4406

A three-dimensional self-consistent photoionization code is developed in order to build more realistic models for asymmetric and/or inhomoge neous photoionized nebulae. With these models the assumption of spheri cal or plane-parallel symmetry can be dropped and models with various geometries can be treated. The gaseous region is divided into numerous cubic cells. The physical conditions in each cell are obtained taking into account the effect of the optical depth and the diffuse radiatio n, which depend on the other cells. In order to compare to observation al data, line intensities are calculated for the whole nebula, as well as for regions covered by a given slit. Isophotal maps are also obtai ned. A model for IC 4406, which is a typical example of bipolar planet ary nebula, is presented. The model assumes a torus of dense material around the central star, as suggested by Sahai et al. Its presence is confirmed by the model, in particular by the shape of the theoretical H alpha + [N II] isophotal map. The chemical abundances required to ex plain the observed line intensities indicate that the chemical propert ies of this bipolar nebula are not characteristic of type I planetarie s.