Electron Densities in Planetary Nebulae

Emissivities are tabulated for lines of [O II] (configuration 2p³) and [S II], [Cl m], [Ar IV] and [K v] (configuration 3P³), using the most accurate atomic data available. The intensity ratios $$R\,=\,I(^2{D}_{3/2}\rightarrow ^4S)/E(^2{D}_{5/2}\rightarrow ^4S)$$ are sensitive to electron density. Densities are obtained from observed ratios in eleven planetary nebulae. The results obtained from [O II], [S II] and [Cl m] are in good agreement. Larger densities are obtained from [Ar IV] and [K v] in high excitation planetaries; this may be evidence for large-scale density variations.