Weisberg AST-9530710 Radioastronomical studies of the interstellar medium and pulsars will be carried out. Observations will be conducted at the Arecibo Observatory in Puerto Rico, the Parkes radio telescope in Australia, the Green Bank Telescope in West Virginia, and the Very Large Array in New Mexico. In particular, the upgraded Arecibo Observatory telescope and the Green Bank Telescope will be highly sensitive instruments that will enable one to make much more sensitive observations than previously possible. The interstellar medium studies are divided into three main categories: In the first, neutral hydrogen line absorption spectra of distant pulsars will be obtained and measured and kinematic distances will be determined from these spectra. The electron densities along the pulsar-Earth lines of sight will then be derived from distances and dispersion measures, and models of the Galactic distribution of electrons will be compared with these results. In the second category, the spatial structure and physical properties of interstellar hydrogen will be studied with neutral hydrogen line absorption measurements of high- latitude and nearby pulsars and recombination line observations in the directions of pulsars. The third category consists of studies of the Galactic magnetic field through Faraday rotation measurements of polarized pulsar signals. Temporal and small- scale spatial variations will be studied in one experiment, while the broad structure of the magnetic field will be investigated in another. There are also three main categories of intrinsic pulsar investigations: First, full Stokes parameter pulsar polarization profiles will be measured and calibrated, and morphological classifications will be assigned on the basis of these and all other published observations. Second, polarized profiles will be examined for temporal variations that could indicate free precession or intrinsic beam changes as well as the Galactic magnetic field variations di scussed above. Third, the emission beam geometry will be studied via empirical/geometrical analyses and fits of the rotating vector model to measured position angles. Undergraduate students at Carleton College will be involved in the research program.
