Stellar Populations in the Magellanic Clouds
A Dissertation submitted in partial satisfaction of the requirements for the degree of
DOCTOR OF PHILOSOPHY
in
ASTRONOMY AND ASTROPHYSICS
by
Jason Robert Harris
December, 2000
Abstract:
Our Magellanic Clouds Photometric Survey has provided UBVI
photometry of millions of stars in both the Large and Small Magellanic
Clouds. We use these data to construct a
detailed picture of the structure and evolution of the Clouds. We
first examine the complexity of interstellar extinction in the Clouds,
and present empirical methods to correct the photometry for
extinction. Our detailed extinction correction includes differential
extinction, spatial variability, and population age dependence. We
next turn our attention to the distribution and dynamical evolution of
stellar populations. Angular correlation functions of main-sequence
stars in the Large Magellanic Cloud reveal large-scale hierarchical
structure among young stellar populations. These structures are
generally gravitationally unbound, and we find that they diffuse
toward a more uniform distribution on a several hundred million year
time scale. A detailed understanding of interstellar extinction and
dynamical evolution of stellar populations are necessary precursors to
the main goal of the dissertation: the star-formation history of the
Magellanic Clouds. We develop and present an algorithm for
determining the best-fit star-formation history of any mixed stellar
population, from its multicolor stellar photometry. The algorithm is
flexible and robust, and includes an accurate appraisal of the
statistical errors of the fit. Finally, we apply the algorithm to our
Small Magellanic Cloud photometry. The resulting star-formation
history of the Small Magellanic Cloud is the most detailed and
complete reconstruction of this galaxy's evolution performed to date.
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