Abstract
This paper continues our study of the behaviour of near-infrared helium recombination lines in planetary nebulae. We find that the 1.7007-μm He i line is a good measure of the He i recombination rate, since it varies smoothly with the effective temperature of the central star. We were unable to reproduce the observed data using detailed photoionization models at both low and high effective temperatures, but plausible explanations for the difference exist for both. We therefore conclude that this line could be used as an indicator of the effective temperature in obscured nebulae. We also characterized the nature of the molecular hydrogen emission present in a smaller subset of our sample. The results are consistent with previous data indicating that ultraviolet excitation rather than shocks is the main cause of the molecular hydrogen emission in planetary nebulae.
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