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Abstract
Low and intermediate mass stars in the final stages of stellar evolution eject their circumstellar envelopes as planetary nebulae, thereby enriching the ISM in processed material and dust. The nature of the grains in planetary nebulae has important consequences for the evolution of the ISM and the stellar population of the Galaxy.
A powerful probe of the dust properties of planetary nebulae is spatial imaging at infrared wavelengths with cryogenically-cooled array detectors. High-resolution (0.8$\sp{\prime\prime}$) 8-13 micron images of a sample of planetary and proto-planetary nebulae have been obtained with the NASA/GSFC Mid-Infrared Array Camera. The nebulae were observed at five discrete mid-infrared wavelengths which include both continuum emission from warm dust grains and a set of "unidentified" infrared (UIR) emission features. Spatial mapping of continuum and feature emission can help to identify the carriers and emission mechanisms which produce the UIR features.
The thesis is divided into two parts. In Part I, the theoretical foundations of planetary nebula formation (Chapter 1) and infrared emission from dust in planetary nebulae (Chapter 2) are discussed. In Part II, the infrared images for three protoplanetary nebulae (Chapter 3) and three young planetary nebulae (Chapter 4) are presented, and the results of the infrared observations are evaluated in terms of the theoretical considerations discussed in Part I.
