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Ices in star-forming regions: highlights from ISO, laboratory and theory
P. Ehrenfreund 1
1 Leiden Observatory, P O Box 9513, 2300 RA Leiden, The Netherlands
ISO allows to study for the first time the complete inventory of interstellar
ices. We present ISO observations of bright star-forming regions with the
Short Wavelength Spectrometer (SWS) and Long Wavelength Spectrometer (LWS).
First results showed the ubiquitous presence of abundant CO2 ice in space
and provided new insights in the gas to solid ratio of many interstellar
molecules. According to their evolutionary state, young objects show
interstellar ice features such as H2O, CO, CO2, CH4 (and other
minor species), as well as interstellar gas features, such as H2O, CO and
CO2. The more evolved objects are dominated by strong atomic emission
lines and polycyclic aromatic hydrocarbons (PAHs). Using the combined
information of interstellar gas and dust in comparison with laboratory results
and theoretical models we determine the line-of-sight conditions towards
massive star formation regions. We constrain gas/grain interactions,
temperature and irradiation conditions and discuss the ISO spectra between 2.5
- 200 
m of star-forming regions in the context of their evolution. Well
established abundances of interstellar molecules will guide the interpretation
of past and future cometary observations. These new ISO results thus allow to
study the connection between interstellar and cometary dust and consequently
provide constraints on the formation of the Solar System.
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