Observations of the unidentified 3.3 microns emission feature in compact HII regions

Details Observations of the unidentified 3.3 microns emission feature in compact HII regions Observations of the unidentified 3.3 microns emission feature in compact HII regions

Aug 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983phdt.........6k&link_type=abstract

Ph.D. Thesis Rochester Univ., NY.

Astronomy and Astrophysics

Astronomy

Emission Spectra, H Ii Regions, Infrared Spectra, Interstellar Matter, Nebulae, Astronomical Spectroscopy, Cosmic Dust, Fluorescence, Grains, Hydrogen, Infrared Astronomy, Thermal Emission

Scientific paper

Many objects have been found to exhibit broad emission features of unknown origin at several wavelengths (3.3, 7.7, 8.6, and 11.3 microns). Two theories were proposed to explain these features. One attributes the features to thermal emission from small (a 0.01 microns) grains which can attain relatively high temperatures (T or = 300 K) in HII regions. The other theory attributes the features to fluorescence of various molecules on grain mantles, which are excited by ultraviolet/visible photons from the hot exciting star. By combining radio and infrared observations of compact HII regions and other objects showing the 3.3 micron feature, both theories were re-examined. The observations permit the detailed physical characteristics of each object to be deduced. This is necessary to fully evaluate the plausibility of each theory for any individual nebula. As a result, the thermal emission theory is shown to be suspect on several grounds. The fluorescence model has been revised to include the situation where the fluorescing grains are in a shell of finite thickness, as indicated by the new observations. Futhermore, a major question regarding the fluorescence model, namely that the required efficiency is unfeasibly high, is re-examined and shown not to be a problem for the objects considered.

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