Advances in Infrared Observations of Planetary Nebulae

Abstract

The discovery of infrared continuum emission from NGC 7027 by Gillett, Low, and Stein in 1967 marked the beginning of far infrared observations of planetary nebulae. These early observations verified the predictions (Delmer, Gould, and Ramsey 1967) of infrared fine structure line emission from the SIV ion and also provided a surprise; namely, that the continuum radiation from planetary nebulae was not free-free emission from the gas, but rather that it was thermal emission from heated dust grains. In the ten years which have elapsed since 1967, numerous infrared emission lines have been observed and interpreted in many of the brighter planetary nebulae. In the middle infrared these lines were principally Ne II at 12.8μ, Gillett et al. (1969); SIV at 10.5μ, Holtz, et al. (1971), Gillett, et al. (1972), Aitken and Jones (1973); and AIII at 9.0μ Geballe and Rank (1973) and Gillett and Forrest (1973).