Low-Excitation Atomic Gas in PPNe: Iso Observations of Fir line Emission in O-Rich Objects

Abstract

We present ISO observations of fine-structure atomic lines in the far-infrared (FIR) from a sample of protoplanetary nebulae (PPNe). Only nebulae surrounding stars hotter than 10000 K were detected. We have compared our data with emission models of photodissociation regions (PDRs) and of shocked regions. The dependence of the emission on the stellar temperature, and the good agreement with the PDR models suggest that emission comes from PDRs instead of shocked regions. The [C II] 158 μm line intensity has been used to measure the mass of the low-excitation atomic gas.

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