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Paper: The Nature of Small Interstellar Dust Particles
Volume: 132, Star Formation with the Infrared Space Observatory (ISO)
Page: 15
Authors: Boulanger, F.; Abergel, A.; Bernard, J. P.; Cesarsky, D.; Puget, J. L.; Reach, W. T.; Ryter, C.; Cesarsky, C. J.; Sauvage, M.; Tran, D.; Vigroux, L.; Falgarone, E.; Lequeux, J.; Perault, M.; Rouan, D.
Abstract: I review new perspectives opened by ISO for the study of interstellar dust with a special emphasis on small particles. In particular, we report first results of the analysis of interstellar medium mid-infrared spectra obtained with ISOCAM. ISO observations of interstellar matter have allowed to detect the emission features attributed to Polycylic Aromatic Hydrocarbons (PAHs) over a wide range of physical conditions including cirrus clouds and the low metallicity molecular clouds in the Small Magellanic Cloud. From cirrus clouds to bright reflexion nebulae such as NGC 7023, the mid-infrared emission from photo-dissociation regions is observed to globally scale with the intensity of the radiation field with only small changes in the spectrum shape. This is a remarkable result confirming what is expected for the emission of small particles transiently heated by the absorption of individual photons. We estimate that about 20% of the cosmic carbon is in the form of aromatic hydrocarbons with less than 1000 atoms. The fraction of the cosmic carbon in PAH molecules with less than 100 atoms is only 1%. The ISO spectroscopic and imaging data together with laboratory experiments on very large molecules and small carbon clusters should help to further characterize the nature of the emitting particles.
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