the mid-ir emission (12 and 25um iras bands) of the interstellar medium is produced by populations of small grains emitting during temperature fluctuations. in region of rather low density and strong radiation fields (close to hot stars), 12um emission contrasts can only be explained if small grains are destroyed and or processed by stellar photons. for the large molecule population (pahs) of interstellar dust, two photodissociation mechanisms have been proposed. the detailed molecular processes involved are poorly known, however, and their efficiency in interstellar clouds unknown. on the other hand the same class of objects exhibits a high 25 to 12um emission ratio that cannot be explained by varying the small grains abundances. at present there is no interpretation of this colour behaviour. to better understand the behaviour of small grains in strong stellar radiation fields, we propose to carry out mid-ir spectroscopic observations on low density (10 cm-3), strongly irradiated (more than 50 times the standard interstellar radiation field) regions, away from ionization fronts. a comparative analysis between spectra of regions where small grains photoprocessing is actively underway and regions where it is not, will provide important information on the grain property changes induced by photons and help identify the most abundant products of photodissociation. this latter point will constrain current ideas on the dominant photodestruction processes and allow a quantitative estimate of their efficiencies in the interstellar medium.
Instrument
SWS01
Temporal Coverage
1996-03-13T10:49:03Z/1997-05-16T17:11:23Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, VERSTRAETE et al., 1999, 'MID-IR SPECTROSCOPY OF SMALL DUST GRAINS AROUND HOT STARS PHOTON PROCESSING OF SMALL GRAINS', 1.0, European Space Agency, https://doi.org/10.5270/esa-nb1yzp3
