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UBC Theses and Dissertations

The CFHT open star cluster survey Kalirai, Jasonjot Singh


We have used the Canada-France-Hawaii Telescope to obtain deep and accurate multi-colour photometry of 19 open star clusters in our Galaxy. The quality and size of the data set are unprecedented when compared with previous studies of open star clusters. The clusters in the survey differ in richness, age, metal content and location in the Galaxy and therefore provide a very diverse database for furthering the research in several areas of astrophysics. Some of the key issues which we address include the comparisons between the observational results and up-to-date theoretical stellar evolutionary models, star cluster dynamics, distance and age determinations, chemical evolution scenarios, and star formation histories. Of particular interest is the study of the properties of white dwarf stars, such as the initial-final mass relationship and the upper mass limit to production. The depth gained in the present survey (limiting V magnitude ~ 25) has allowed us to establish a large catalogue of white dwarf candidates, and our current spectroscopic investigations will provide the much needed observational constraints to white dwarf theoretical models. The colour-magnitude diagrams for the rich, young clusters in the survey possess very tightly constrained, long main-sequences and show a much richer cluster population than previous studies. This thesis summarizes how this was done as well as key results for the two richest clusters in the survey, NGC 6819 and NGC 2099. For NGC 6819 we find: distance = 2500 pc, age = 2.5 Gyrs, size = 9.5', and mass = 2600 M⊙. The cluster is found to be dynamically evolved and exhibits mass-segregation effects. A strong cooling trail of white dwarfs is found to be in excellent agreement with a 0.70 M⊙ theoretical white dwarf cooling model. For NGC 2099 we find: distance = 1500 pc, age = 0.5 Gyrs, size = 13.9', and mass = 2500 M⊙. The cluster exhibits some signs of dynamical evolution, although not as severe as for NGC 6819. The white dwarf cooling age of NGC 2099 is found to be in excellent agreement with the turn-off age.

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