The Diffuse Interstellar Medium: Magnetic Fields, Physical Parameters and Morphology

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AST 0406987HeilesThis project directed by Dr. Carl Heiles concentrates on measuring physical parameters of the diffuse interstellar medium, which is the matrix within which molecular clouds reside and the medium that soaks up the energy from massive stars as they rapidly evolve to their deaths. Accordingly, it is the medium through which the feedback processes linking stellar birth and death must operate. His interest is clarifying these processes by determining the physical aspects of the diffuse atomic hydrogen (HI) using the radioastronomical techniques with which he is expert. These techniques provide unique information on magnetic field strength, temperature, kinematics, and morphology. He will cover a wide range of size scales, from small dense molecular clouds to the global galactic scale. These studies, together with their comparison with the relevant theories, are crucial for understanding the thermodynamics, magnetogasdynamics, and dynamo processes of the interstellar gas. The present time is particularly appropriate for these studies because the Green Bank Telescope (GBT) has become operational and Arecibo, with its filled aperture and high angular resolution, provides excellent maps. At Arecibo, the mapping will be greatly enhanced by the multifeed array, called ALFA, which should come on line midway through the period covered by this award.In the past Dr. Heiles has worked closely and intensively with the national radio observatories, NRAO and NAIC, performing calibrations in the realms of fundamental beam properties and polarization. Without these efforts, these observatories would not have polarization capability. This tradition will continue. At the GBT the spectral correlator will become usable for polarization work, and Dr. Heiles will calibrate it and develop software for its use. At Arecibo, he will continue his deep involvement with technical details of calibrating the multifeed array system. Also, he will continue our cross-fertilization of undergraduate education andresearch.