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Red fluorescence and 3-12 micron emission in NGC 2023, HD 44179, M 82, and Lynds 1780A red excess observed in the Red Rectangle (HD 44179), was attributed to a possible molecular fluorescence mechanism was discovered in NGC 2023 and analyzed in subsequent work in this and other nebulae. An unexpected red light excess was also noticed in a high latitude dark cloud L 1780. The fluorescence was attributed to hydrogenated amorphous carbon by Duley (1985), on the basis of laboratory work. Alternatively, transitions between electronic states of free polycyclic aromatic hydrocarbon molecules, by-passing the cascade along the vibrational states was considered. In L 1780, the red excess was related to the 12 micron emission detected by IRAS. A quantitative comparison of the intensity of the red fluorescence and that of the 3 to 12 micron features is thus warranted in helping assess the physical properties of large interstellar molecules. The red fluorescence radiation, F(R), appears as a bump on the spectra between 0.6 and 0.9 micron. Values were deduced from the spectra for HD 44179, and for the high latitude cloud L 1780. Corrections for the extinction, both interstellar and internal to the nebulae, were included. The 3 to 12 micron brightness, F(IR), was obtained through integration of the spectra for NGC 2023, and for HD 44179 after removal of a smooth continuum due to hot large grains. The values of the ratio of fluorescence flux to the infrared flux, F(R)/F(IR), are summarized. Red fluorescence and infrared radiation are two separate ways to access to the size of the molecules through observation, and it is rewarding that both approaches give similar results. These findings bring a striking coherence into the physical description of the particles, and add further support to the initial attribution of the infrared features to polycyclic aromatic hydrocarbons (PAHs).
Document ID
19910005611
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Ryter, Charles (Commissariat a l'Energie Atomique Gif-sur-Yvette (France)., United States)
Dhendecourt, Louis B. (Paris VII Univ.)
Date Acquired
September 6, 2013
Publication Date
December 1, 1989
Publication Information
Publication: NASA, Ames Research Center, Interstellar Dust: Contributed Papers
Subject Category
Space Radiation
Accession Number
91N14924
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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