Radiative Transfer Modeling of Water

Water is one of the most important molecules in star-forming interstellar clouds. Only present in trace amounts in cold molecular clouds, it becomes the third most abundant species (after molecular hydrogen and helium) in regions heated by newly formed stars. With this more than 10,000-fold abundance variation, the water emission- and absorption-line spectrum offers a unique probe of the physical structure of star-forming clouds and of the fundamental interaction between gas and grains in such regions. Furthermore, study of the water spectrum may prove essential to understand the energy balance in these clouds.

Largely inaccessible from the ground, the water spectrum of astrophysical sources will be prime targets of the Herschel Space Observatory and its Heterodyne Instrument for the Far-Infrared (HIFI), to be launched by the European Space Agency in 2007. A HIFI key project is currently being defined focusing specifically on water in star-forming regions (led by van Dishoeck, Leiden, NL), and many open-time proposals involving water-line observations are also foreseen.

This workshop brings together experts in the field of radiative transfer modeling and astrophysical spectroscopy of water, both from within and outisde the HIFI consortium. The overall aim of the workshop is to better understand the excitation and line-formation mechanisms of water in astrophycisal environments, which will be essential to fully exploit the planned HIFI observations. In particular, at the workshop the participants will compare and validate the existing techniques for modelling the water-line spectrum, and explore the diagnostic potential of various lines in probing different physical and chemical conditions likely to be encountered in interstellar clouds.

The organisation of this workshop will be carried out by Michiel Hogerheijde (Leiden, NL), Edwin Bergin (University of Michigan, USA), Jose Cernicharo (IEM, Spain), Frank Helmich (SRON, NL), David Neufeld (Johns Hopkins, USA), Floris van der Tak (MPIfR, Germany), and Jeremy Yates (University College London, UK).