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Ph.D. (McMaster University, 2001)

Title: A Polarimetric Study of Magnetic Fields in Star-Forming Molecular Clouds
Advisor: Dr. Christine D. Wilson

I have used a recently commissioned, highly sensitive polarimeter at the James Clerk Maxwell Telescope to probe the magnetic field geometries of six star-forming regions within 500 pc of the Sun. For five of the regions, these are the first data produced of emission polarization from dust grains aligned by local magnetic fields. The variations in the polarization pattern across the clouds have been compared to predicted patterns from various models of magnetized molecular clouds. In several regions, particularly OMC-3 in the Orion A cloud, the polarization data are very consistent with predictions of a recently developed model of filamentary molecular clouds threaded by helical fields. The regions of NGC 2068 and LBS 23N could also contain helical magnetic field geometries. Although NGC 2024 is successfully modeled by a helical field, this geometry is not consistent with existing data of the line-of-sight magnetic field, which is not probed by polarization measurements. Instead, I suggest that the field geometry in NGC 2024 is that of an expanding ionization front from the associated HII region, bent around the dense ridge of star-forming cores. Prior to this work, most regions were thought to contain uniformly oriented magnetic fields. Only one region in my sample contains a distribution of polarization vectors which could support such a geometry; in this cloud, Barnard 1, I have estimated the three-dimensional field strength and orientation associated with this uniform field and find a significant fraction of the field lies in the plane of the sky. This solution applies only to low column densities and not to the denser cores within Barnard 1, which do not exhibit alignment with the low density material. In short, this work reveals that uniform field geometries are not supported on intermediate scales within molecular clouds. Furthermore, no single magnetic field geometry is applicable in all molecular clouds; in each region, local environments and the associated physics must be taken into account.

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M.Sc. (University of Calgary, 1996)

Title: G55.0+0.3: A Highly Evolved Supernova Remnant?
Advisor: Dr. A. Russell Taylor

In order to determine the nature of an object identified as a potential supernova remnant in a 327 MHz survey of the Galactic plane, continuum data have been taken at 1420 MHz with identical resolution to that of the survey. Additionally, HI spectral line data have been taken in order to determine the distance to the object.

Multifrequency analysis shows that a shell feature in the southern part of this object is nonthermal and confirms earlier studies that identified the northern portion as an HII region. The nonthermal nature of the shell and the absence of infrared flux density confirms the speculation of Taylor et al. (1992) that this object, G55.0+0.3, is a supernova remnant (SNR). From analysis of atomic hydrogen, its estimated distance is 14 kpc, yielding a radius of 62 pc. This makes it one of the largest known of this class of objects. Additionally, an age estimate of one million years exceeds the conventional limits in the literature by a factor of five. There also exists compelling evidence that the remnant could in fact be associated with the nearby pulsar, J1932+2020.

The discovery of G55.0+0.3 implies that the radiative lifetimes of SNR could be much longer than previously suggested. The proposed pulsar/SNR association is older than any previously documented by an order of magnitude. If valid, it suggests that searches for associations should not be restricted to the regions about young pulsars.

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Last Updated October 5, 2002