The following document lists the file abstract/FBERTOLD_PDR_PHYS.abs
from catalogue VI/111.
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In order to study the physical conditions in low-excitation photodissociation regions we propose a detailed spectroscopic study of two bright H2 emission knots in the "prototypical" reflection nebula NGC 2023. A first analysis of our SWS observations of the S140 PDR (Timmermann et al. 1996, attached) motivates us to also request followup observations of S140 to clarify questions raised regarding the gas temperature, the ortho-para ratio, and the iron abundance. To comparatively study PDRs from significantly harder radiation fields and the effects of rapidly propagating ionization fronts on the PDR structure we propose to observe several molecular clumps illuminated by early type O stars. For this we selected targets in the W5 and Rosette HII regions.