SIMBAD references

We have obtained spatially resolved intermediate-dispersion spectroscopy observations for a sample of extended planetary nebulae (PNe) representative of different morphological classes. The study has included multiple shell PNe (M 1-46, NGC 2438, NGC 5882 and NGC 6720), bipolar PNe (K 4-55, M 1-75, NGC 2440 and NGC 2818) and hydrogen-poor PNe (A 30 and A 58). The information oobtained has allowed an analysis of the chemical composition gradients in the ionized gas. In particular, we have specially studied the He/H, N/O y Ne/O ratios. A comparative study of the chemical abundances and physical properties of the haloes and main nebulae of the multiple shell PNe has been carried out. In addition, spatially-resolved high-dispersion spectroscopy data were obtained for M 1-46 and NGC 6720, thus allowing an analysis of their kinematics and 3- dimensional structures, and a detailed knowledge of the loss-mass history.