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Title:
Far-Ultraviolet Studies of H2 in Photodissociation Regions
Authors:
France, Kevin; McCandliss, Stephan R.; Burgh, Eric B.
Affiliation:
AA(Center for Astrophysics and Space Astronomy, University of Colorado, 593 UCB, Boulder, CO 80309), AB(Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218), AC(Center for Astrophysics and Space Astronomy, University of Colorado, 593 UCB, Boulder, CO 80309)
Publication:
FUTURE DIRECTIONS IN ULTRAVIOLET SPECTROSCOPY: A Conference Inspired by the Accomplishments of the Far Ultraviolet Spectroscopic Explorer Mission. AIP Conference Proceedings, Volume 1135, pp. 198-203 (2009). (AIPC Homepage)
Publication Date:
05/2009
Origin:
AIP
PACS Keywords:
Molecular clouds, H2 clouds, dense clouds, and dark clouds, Astronomical observations, Spectroscopy and spectrophotometry
DOI:
10.1063/1.3154049
Bibliographic Code:
2009AIPC.1135..198F

Abstract

We present a brief review of molecules studied with far-ultraviolet spectroscopy, discussing absorption line measurements of the dominant interstellar molecules (H2 and CO) and H2 emission from molecular clouds near hot stars. We give two examples where the CO/H2 ratio, which can only be derived uniquely in the far-ultraviolet, can be used to study the structure of the interstellar medium. Prospects are discussed for future work with deeper observations that would allow one to probe farther into molecular clouds in the galaxy. We describe a mini-survey of five local photodissociation regions (PDRs) carried out with FUSE. We use these data to characterize the far-UV spectra of PDRs for the first time and to refine models of the H2 fluorescent emission process. We find that our models can adequately reproduce the observed emission spectra of three of these regions (IC 63, M42, and IC 405). The remaining two (NGC 2023 and NGC 7023) do not show clear emission from H2 in the FUSE band, despite the well defined and characteristic double-peaked emission features at 1575 and 1608 Å observed in archival observations, as well as the clear fluorescent signatures in the well studied near-IR rovibrational emission lines, thus suggesting a more complex radiative transfer scenario in these environments. We conclude with simple simulations showing the potential gains that could be made in the studies of PDRs with future far-ultraviolet spectrographs with increased effective area and resolving power over current instruments.
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