H_2_ infrared line emission from S 140: a warm PDR.
Draine, B. T.; Bertoldi, F.; Sternberg, A.; Wright, C. M.; Drapatz, S.; Timmermann, R.; Haser, L.
Abstract
ISO SWS spectra of H_2_ pure rotational and ro-vibrational transitions, as well as [FeII], and [SiII] fine structure lines were obtained for one position on the photodissociation region (PDR) adjacent to the bright rim of the S 140 HII region. The gas density is =~10^4^cm^-3^ and the incident UV flux χ=~400 at the location of the ionization front. Our PDR model analysis shows that the relative H_2_ line intensities are characteristic of low-density fluorescent emission and that the gas temperature is T>500K in the partially dissociated gas. A comparison of predicted and observed fine structure line intensities permits an estimate of the abundances of Fe and Si.