Radiative transfer simulation of water rotational excitation in comets

Context.The recent advent of space-based detectors at far-infrared and submillimetre wavelengths opened up the possibility of observing cometary water from its rotational transitions. The 110-101 fundamental line of ortho H2O at 557 GHz was detected in several comets by the Submillimeter Wave Astronomical Satellite and Odin. This line as well as other water and HO lines will be observed by the three instruments of the ESA Herschel Space Observatory. In order to prepare or interpret these observations, excitation models including H2O self-absorption are required.