This grant supports Dr. Elitzur's research on projects which share the common theme of application of radiative transfer techniques for line analysis in various astronomical environments. The topics include studies of star forming regions; the envelopes of late-type stars; and photoionized regions, such as the accretion disks of cataclysmic variable stars. The structure of and physical conditions in these various astronomical objects will be studieed from their line emission in the ultraviolet, optical, infrared, and radio spectral regions. Dr. Elitzur applies radiative transfer techniques to four specific topics. (1) The polarization of line radiation provides important information on the properties of the source where it was generated. A solid theoretical framework is needed to interpret the observational data. (2) Two of the more prominant properties of star forming regions are strong maser emission from hydroxyl and water vapor and powerful outflows of material. The theoretical implications of both issues are addressed by Dr. Elitzur. (3) In the area of late-type stars a long range goal of Dr. Elitzur's research is the construction of a coherent picture for the outer envelopes, where a multitude of interesting effects are observed. (4) The study of accretion disks has steadily gained importance in the last few years with the mounting evidence that disks are a common occurrence in astronomical systems of all scale sizes.
