Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19410904k&link_type=abstract
American Astronomical Society Meeting 194, #109.04
Astronomy and Astrophysics
Astronomy
Scientific paper
We obtained high resolution optical spectra of the illuminating stars in two reflection nebulae, NGC 2023 and vdB 102. Such observations probe the photodissociation regions (PDRs) in front of the stars. Ground-based measurements of the atoms, Na I and K I, and the molecules, CH, CN, and C_2, were analyzed to extract the physical conditions present in each PDR. Estimates of the gas density, gas temperature and flux of ultraviolet radiation were derived and compared with the results from infrared and radio studies. The conditions derived are similar to those found in these previous studies. The foreground material is less dense than the gas in the molecular cloud behind the star(s). The gas temperature was set at 30 K since the temperature had a negligible effect on the chemistry and since this is the temperature inferred for the foreground PDR toward HD 200775, the illuminating source of NGC 7023. The flux of ultraviolet radiation was found to be less intense than in the molecular material. The columns of Na I and K I were reproduced when the extinction curve for the line of sight was adopted. Future studies should include the effects of the specific extinction curve when modeling reflection nebulae and their associated photodissociation regions.
Federman Steven Robert
Knauth David C.
Lambert David L.
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