Brown Dwarfs and UKIDSS

In this thesis I present the work of two studies into the population of low-mass stars and brown dwarfs within the open galactic clusters of Praesepe and Blanco 1 using optical and infrared photometry. Observing these objects within clusters is of great importance as their known ages and distances allow for comparisons to be made between the observed results and those predicted from theoretical formation and evolutionary models, whilst expanding our understanding of the initial mass function. Following an introduction to the formation, evolution and observational history of brown dwarfs in Chapter 2 an overview of the principle data reduction processes and instruments used in this thesis is given in Chapter 3. Chapter 4 presents the result of the survey carried out in Praesepe using archival 2MASS, SDSS and UKIDSS data in a range of filters. Proper motion information is combined with colour magnitude cuts to select out and classify objects that are considered to be cluster members. Over 280 members have been identified with a cluster mass function that is consistent with the values presented for other clusters found. This mass function is in disagreement with previous values found for Praesepe. Chapter 5 presents the results of a follow up J band survey using WFCAM to the CFHT12k I and z survey of Moraux et al. (2007). The data reduction and membership selection procedure are discussed with 27 low-mass objects found to be members. Chapter 6 in contrast to the previous chapters presents a study not of brown dwarfs but of a suspected main-sequence, magnetic white-dwarf binary system found during an archival search of the UKIDSS DR3 database for objects with unusual Y band colours. The evidence for this system being a Polar is presented along with a discussion as to the assumed system properties. Follow up observations using the IAC-80 telescope, UKIRT and the SWIFT satellite are also presented. Finally in Chapter 7 I summarise the results from each chapter and identify areas of future work.