Theoretical Studies of Astronomical Masers

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ABSTRACTElitzur, MosheAST-9819368The high-resolution data now obtainable from the Very Long Baseline Array (VLBA) radio facility and wide-field data from the Infra-Red Astronomical Satellite (IRAS) and Infra-red Space Observatory (ISO) have provided a wealth of new information on naturally occurring maser processes. The extended atmospheres of both young and dying stars, the expanding debris of supernova remnants, and the large star-forming regions in other galaxies are all much brighter in the infrared and microwave region than their physical temperatures would imply, suggesting that maser activity is occurring. Molecules such as H20, OH and SiO are energetically 'pumped' by the IR radiation emitted by hot dust or, in some cases, by direct collisions with neutral 'wind' particles. Such species release this energy in the form of specific well-collimated long-wavelength photons. These are crucial processes to understand, since a large fraction of most stars' mass is returned to the interstellar medium under such conditions. This grant supports a theoretical study of a broad variety of astronomical maser sources. The computed models will take into account the photon radiation and hydrodynamic pressure, accelerations and heating of dust. The goal is to achieve a good agreement between observations and models by including thermal energy balance computations into the existing code.