SIMBAD references

The planetary nebula NGC 2392 possesses an extremely unusual spectrokinematic morphology, characterized by several strange and elusive structures. In this paper, extensive narrowband imaging of the source is used to investigate the shell excitation structure, while [O III] and [S II] images are ratioed to provide fully sampled mapping of electron density and temperature. As a result, we are able to confirm the presence of low densities in the various filamentary structures, an appreciable radial decrease in density in the outer shell, and finally, a probable regime of higher shell densities at the interface of the bright inner shell and lower intensity outer halo. Although temperatures are more uniform, we also find evidence for a significant temperature enhancement close to the inner-outer shell interface, and it is proposed that both anomalies (in density and temperature) arise in a postshock cooling regime. Finally, present imaging and prior spectroscopy are used to construct a revised model of the source, in which it is argued that the outer filamentary structure occupies a disklike regime, congruent with the principal plane of the outer spheroid. Individual filaments arise from low-excitation density contrasts, created through the interaction between the outer shell and a precessing jet.