St. Mary's University Thesis Abstracts

The Star Forming Core of Mon R2

Jean Giannakopoulou

M.Sc. Thesis, Saint Mary's University

1993 September

Thesis Supervisor: George F. Mitchell

In this thesis, the nature of the star forming core of the Mon R2 cloud is investigated using new, high spatial resolution observations. The new data include: maps of 12CO J=3-2, HCN J=4-3 and H2C0 J(K-1,K+1) =5(1,5)-4(1,4), spectra of 12CO J=2-1 and 13CO J=3-2 at 12 positions, an infrared M-band spectrum, and finally sub-millimeter and millimeter continuum maps (450 microns, 800 microns, 1100 microns and 1300 microns). Based on the spatial distribution of the intensity of the 12CO J=3-2 transition, we present a qualitative description of the region which consists of complexes and clumps. The complexes surround a central area of lower intensity which corresponds to the compact H II region in the cloud core. The radiation from the sub-millimeter and millimeter continuum maps is believed to be due to thermal emission from dust, located in and around the H II region. Some differences between maps are believed to be due to the increasing importance in the millimeter maps of free-free emission from ionized gas.

The complexes incorporate 13 smaller intensity peaks (clumps), which have large masses (2.7 to 0.007 solar masses) and large velocity dispersions (typically 30 km/s). The CO clumps are not distributed in a bipolar fashion. They probably formed from the interaction of the large outflow with the ambient gas. The source of the outflow is not clearly identified. We propose that the outflow could originate from IRS 3, which has gone through a quiescent phase.

The CO excitation temperature, Tex, varies between 5 and 60 K. Although the CO J=3-2 transition can locate the position of the dense gas, it misses a large fraction of the dense quiescent gas (70-80%) due to self- absorption.

The sum of the magnetic and the gravitational energy (12 x 10[45] erg) is somewhat smaller than the total kinetic energy of the inner core of the Mon R2 cloud (15 x 10[45] erg), and hence, the core is either in the process of disruption or in dynamical equilibrium.

Empirical Confirmation of the Mass Dependence for White Dwarf Luminosities

Jeremy R. W. Beckett

M.Sc. Thesis, Saint Mary' University

1993 December

Thesis Supervisor: David G. Turner

Existing calibrations of white dwarf luminosities have invariably relied upon the inhomogeneous sample of refractor parallaxes published in the General Catalogue of Trigonometric Stellar Parallaxes. We have completed a new calibration of white dwarf absolute magnitudes using a compilation of homogeneous and very accurate reflector parallaxes published by the U.S. Naval Observatory. The properties of the stars in this sample are well enough established that statistical luminosity corrections resulting from the combination of parallax errors with the space distribution peculiar to the stars can be established fairly reliably. The resulting luminosity calibration is in very good agreement with previously published results, and is of sufficient accuracy to investigate for the subset of DA-type stars the expected dependence on surface gravity (or mass) predicted theoretically from the white dwarf mass-radius relation. The results are in complete accord with expected results, which indicates that a full knowledge of the luminosity for any DA-type white dwarf requires information on its surface gravity as well as effective temperature. A byproduct of this study is a new estimate for the distance to the Hyades cluster, which contains several member DA stars.

Neutrino Oscillations as an Explanation for the Solar Neutrino Problem

David C. Taylor

B.Sc. Thesis, Saint Mary's University

1994 May

Thesis Supervisor: Malcolm N. Butler

One possible solution to the solar neutrino problem is that neutrinos may have mass, which leads to the possibility of one flavour of neutrino converting to another as it travels from the Sun to the Earth. We are investigating the possibility that all three known flavours of neutrinos are involved in this process, and whether the signals that are seen in Earth- based solar neutrino detectors can be used to differentiate the many theoretical models for the neutrino mass hierarchy. The Zee model is a simple case to explore the possible reasons for the discrepancy in the observed solar neutrinos. This model requires at least one of the neutrinos to have mass and then flavour changing can occur between neutrinos.

Oblique Magnetic Fields in Cosmic-Ray Mediated MHD Shocks

Jonathan Dursi

Honours B.Sc. Thesis, Saint Mary's University

1994 May

Thesis Supervisor: David A. Clarke

In this report, the results of several time-dependent numerical simulations, based on the two-fluid model, of cosmic-ray mediated MHD shocks are presented. One- dimensional shocks with magnetic fields oblique to the shock normal are examined. The dependence of the shock structure on the angle between the magnetic field and the shock normal, and the magnitude of the ambient magnetic field is investigated.

It is found that for weak fields the orientation of the B-field plays only a very small role, whereas for stronger fields,there is a large directional dependence. The orientation can strongly influence the transient features of the shock structure, but the steady-state values are almost unaffected, even in stronger fields. Furthermore, in the one-dimensional case, the orientation of the magnetic field will affect the "effective" Alfven speed of the fluid, as only the perpendicular component of the magnetic field will contribute to signal speed. The cosmic ray acceleration efficiency is found to depend on the angle, as a strong perpendicular component of the magnetic field will act to decrease the acceleration efficiency. There is no dependence on the parallel component of the magnetic field.

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