The Physical and Chemical Properties of Circumstellar Matter

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9314408 Huggins Many luminous red giant stars eject significant amounts of material from their outer layers. The star then evolves rapidly into a white dwarf while the matter is seen for a time as a planetary nebula. It is now known that the star and the visible nebula are surrounded by a large shell of neutral gas. The properties and evolution of these shells will be studied by observing their molecular emission at millimeter and sub-millimeter wavelengths. This information will be used to develop a description of the formation and evolution of the nebulae. These studies should substantially improve our understanding of this important but little understood phase of stellar evolution. ***