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Photodissociation Regions and Planetary Nebulae

Published online by Cambridge University Press:  07 August 2017

A.G.G.M. Tielens
A.G.G.M. Tielens*
Affiliation:
MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA

Abstract

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FUV photons (<13.6eV) from the central star create a region of warm (≈1000K) atomic and molecular gas around Planetary Nebulae (PN). This paper reviews theoretical and observational characteristics of such regions, commonly called photodissociation regions or PDRs. PDRs around PN differ in some aspects from those in other galactic objects and this is briefly discussed with an emphasis on time dependent effects. It is concluded that, in evolved PN (texp>103 yr), molecules will only survive inside dense clumps (>106 cm−3). H2 emission from such dense gas will show a thermal spectrum in the low v states. Finally, the physical conditions in the PDR associated with NGC 7027 are compared to those in other galactic and extragalactic PDRs

Type
III. Highlights on the Nebulae
Information
Symposium - International Astronomical Union , Volume 155: Planetary Nebulae , 1993 , pp. 155 - 162
Copyright
Copyright © Kluwer 1993 

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