SIMBAD references

We have observed the high excitation planetary nebulae NGC 7027, NGC 6543 and the low excitation planetaries Hu 2-1 and Cn 3-1 in the optical & near IR with the aim to contribute accurate measurements of their gaseous iron abundances. Use was made of multi-level atomic models of iron ions to interpret the observed forbidden lines of various iron ions. The resulting total abundances are: N(Fe)/N(H)=(4±2)x10^–7, (3±2)x10^–6, (9±4)x10^–7, (6±3)x10^–7, in NGC 7027, NGC 6543, Hu 2-1, Cn 3-1, respectively. They are believed to be more accurate than previous determinations for NGC 7027 & NGC 6543 (no previous data were available for the other two PNe). The corresponding depletion factors are 80, 11, 36 and 53, respectively. We don't see in this limited sample of PNe any indication that the depletion factors are linked with properties like the excitation of the nebula or its age.