Interpretation of the neutral helium triplet spectrum in planetary nebulae

Citation

Persson, Sven Eric (1972) Interpretation of the neutral helium triplet spectrum in planetary nebulae. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-08212008-101113

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

The theory of the He I triplet spectrum is modified to include the effects of solid particles within the ionized regions of planetary nebulae. New observations of the emission lines [...]5876, 7065, and 10830 are presented for over twenty nebulae, extending the list of objects studied previously by O'Dell. The empirical ratios [...] and [...] are combined with the theory to study the discrepancies between the He I [...] depopulation rates D[...](derived from R[...]), D[...](from R[...]), and D[...] (theoretical). If the presence of dust is neglected, the discrepancies are such that D[...] > D[...] > D[...], in most cases. This is essentially the result found earlier by Capriotti for a smaller sample of objects. Estimates of [...], the [...]10830 dust optical depths which force D[...] = D[...], are derived by accounting for the resonance trapping and dust absorption of the [...]10830 radiation. These estimates are consistent, on an order-of-magnitude basis, with values implied by observed infrared excesses in planetary nebulae, and by simple models of reradiating dust shells.

The important effects of nebular structural features upon the He I triplet spectrum are studied theoretically and observationally. Overall correlations between the apparent [...] depopulation rate discrepancies and nebular parameters are shown to have a connection with a wide range of nebular problems.

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