Interpretation of the Neutral Helium Triplet Spectrum in Planetary Nebulae

Author: Persson, Sven Eric

Year: 1972

Degree: Dissertation (Ph.D.)

Advisor: Münch, Guido

Committee Member: Unknown, Unknown

Option: Astronomy

DOI: 10.7907/FNVG-6W53

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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