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UBC Theses and Dissertations

An analysis of stellar populations in globular clusters Goldsbury, Ryan


This thesis is composed of three chapters, as well as an introduction, which describe three distinct projects. In Chapter 2 we present new measurements of the centers for 65 Milky Way globular clusters. Centers were determined by fitting ellipses to the density distribution as well as the symmetry of the clusters. All of the determinations were done with stellar positions derived from a combination of two single-orbit Advanced Camera for Surveys images of the core of the cluster. We find that the ellipse-fitting method provides remarkable accuracy over a wide range of core sizes and density distributions, while the symmetry method is difficult to use on clusters with very large cores, or low density, requiring a larger field, or a very sharply peaked density distribution. Chapter 3 deals with a re-analysis of previous work on white dwarf natal kicks, and expands on this to analyze the radial distributions of stellar populations in globular clusters at earlier stages of stellar evolution (earlier referring to pre-white dwarf). The effects of stellar incompleteness, and a method to account for this are discussed. Finally, the results of a statistical analysis of completeness corrected radial distributions in 56 globular clusters are presented. No significant evidence of kicks is found, however multiple clusters show evidence that stars along the horizontal branch have not relaxed since undergoing mass loss after leaving the main sequence. In Chapter 4, we present a novel method for determining the distance to a star cluster by fitting spectral energy models to the spectral energy distributions of cluster white dwarfs in multiple filters. The statistics of our fitting method are discussed in detail. This approach results in a true distance modulus of (m-M)₀ = 13.35 ± 0.02 ± 0.06, which corresponds to a physical distance of 4.67 ± 0.04 ± 0.13 kpc. The first error given is random, and the second is systematic.

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