Hyades, Pleides and Taurus Brown Dwarfs

This thesis describes the search for brown dwarfs in Hyades and Pleiades open clusters and in the Taurus star forming region. Initial surveys were carried out with deep CCD observations. Infrared follow up work was then used confirm membership status. A first chapter provides a brief introduction to the fundamental properties of brown dwarfs and highlights the reasons why it is important to study them. The second chapter gives a current review of the theory of brown dwarfs and describes recent searches for brown dwarfs and their results. Chapter 3 then describes the basic principles of photometry, reviews the instrumentation in use and describes the data reduction techniques necessary for analysis. The results of the three projects carried out throughout the course of this Ph.D. are presented in chapters 4, 5 and 6. Chapter 4 presents a deep, large area, optical IZ survey of the Hyades in which no candidate brown dwarf members remain after follow up infrared JHK photometry, optical spectra and proper motion measurements. Chapter 5 presents the results of a deep CCD IZ survey of the Pleiades with follow up infrared K photometry implemented to confirm cluster membership. Luminosity and mass functions for the cluster are then derived with the mass function found to be slightly rising across the stellar/sub-stellar boundary as has been evident in recent work (Bouvier et al. 1998, Martin et al. 1998, Hodgkin & Jameson 2000). Chapter 6 presents the very preliminary results of a partial area reduction of a deep CCD RIZ survey of the Taurus star forming region with candidate member finder charts provided in Appendix A. Some 88 isolated brown dwarf candidates are found with masses down to 7Mjupiter. Further work will be needed to verify the status of these objects. Chapter 7 summarises the important conclusions from chapters 4, 5 and 6 and also give suggestions for future work.