Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........8d&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SANTA BARBARA, 1995.Source: Dissertation Abstracts International, Volume: 56-08, Sect
Astronomy and Astrophysics
Astronomy
1
Vela Pulsar, Gum Nebula, Galactic Magnetic Field
Scientific paper
Interstellar turbulence spans more than 7 decades of spatial scales in the interstellar medium. This turbulence produces fluctuations in the spatial density of interstellar electrons. Radio-waves emitted by astronomical objects diffract around these density fluctuations to arrive at the Earth from many directions. The apparent angular sizes of compact sources therefore can appear much larger than their actual angular sizes; this effect is known as angular broadening, and the angularly broadened image is called the scattering disk. Measurements of angular broadening are a powerful tool for characterizing interstellar turbulence: observations of pulsars can constrain the possible locations of the turbulence in the interstellar medium, while observations of interstellar maser complexes can, in principle, completely determine the structure of the turbulence on all spatial scales. I present herein angular broadening measurements at radio-wavelengths, using the techniques of Very-Long -Baseline Interferometry of the Vela Pulsar and the OH maser complex in W49N two strongly scattered Galactic objects. I also present a new model-fitting algorithm, written to analyze the OH maser data, that simultaneously solves for calibration errors while determining the model parameters. I showed that the scattering disk size of the Vela pulsar requires that the associated turbulence be located near the Vela supernova remnant, rather than the much closer, interposed, Gum Nebula, as was previously believed. This result lends considerable support to the theory that supernova remnants generate the interstellar turbulence. I have also discovered that the OH masers in W49N have elliptical scattering disks with major axes approximately aligned and oriented approximately parallel to the Galactic plane. These results imply that the associated turbulence must be anisotropic. The alignment of the scattering disks assures us that the anisotropy is magnetic-field induced, and the fact that the major axes of the scattering disks are perpendicular to the Galactic plane suggests that, specifically, the Galactic magnetic field induce the anisotropy.
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