Surface Brightness Fluctuations in Globular Clusters.

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The focus of this thesis project was to study the spatial surface brightness fluctuations in Galactic globular clusters. This thesis also includes analysis of the color-magnitude diagrams of these clusters taken in V and I. The first important result of this investigation is that the globular cluster fluctuation measurements are not discordant with the empirically determined extragalactic SBF distance scale of Tonry (1991, ApJ, 373, L1), which gives MI as a function of a stellar population's integrated (V - I) _{rm o} color. Another result is that fluctuation colors are related to the metal abundance of a stellar population, and this analysis has made the first attempt at understanding populations in galaxies from their fluctuation colors and the corresponding results in globular clusters. The primary findings of this study of the stellar populations in the centers of globular clusters are that (1) (| V - | I) does not change with radius, (2) | M_{I } is constant among clusters covering a wide range of metallicity, (3) | M_{V } has a dependence on metallicity, (4) there may be some variation in | M with radius in some clusters although we cannot rule out statistical variations as the source, (5) variations with radius that are seen seem to be caused by giant branch changes and not by metallicity variations, and (6) the CMD morphology does not vary with radius with the exceptions of M15 and M92. These results show a possible systematic change in the population of giant stars relative to the entire population as a function of radius within several clusters and possibly among the clusters studied here as a whole. There were two main results from the study of the color-magnitude diagrams. First, the tip of the giant branch in the I band is stable at M_{I, rm tip} = -3.85 +/- 0.10 for the clusters studied. The second result is the identification of a "gap" in the giant branch at MI = -1.75 for the clusters M2, M13, M80, M92, and omega Cen, all of which exhibit a blue horizontal branch morphology. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened with permission of school.).

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