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Title: Searching for benchmark systems containing ultra-cool dwarfs and white dwarfs
Author: Gomes, Joana
Awarding Body: University of Hertfordshire
Current Institution: University of Hertfordshire
Date of Award: 2013
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I here present my search for benchmark systems with main sequence stars widely separated from ultracool dwarfs or white dwarfs. Different near-infrared and optical surveys have been used to create samples of L dwarf candidates from colour cuts and by exploring the faintest limits of available surveys. I started by using the Two Micron All Sky Survey, and then expanded my method in order to include sources from the UKIRT Infrared Deep Sky Survey, which has not yet been fully explored for L dwarfs. In order to search for wide main sequence star companions I have used stars from Hipparcos, Gliese and PPMXL. I then applied a set of selection rules based on photometry and proper motion to find these systems. This search led to the discovery of two new benchmark systems with genuine L dwarfs, that have been spectroscopically confirmed. A large sample of potentially new systems still awaits a complete analysis, and we thus expect more exciting discoveries to stem from the method utilized. A method to identify new late-T and Y dwarfs from the Wide-field Infrared Survey was also been developed, with the aim of using the surveys maximum sensitive limits. The technique relies on objects only detected in the W2-band and through a series of rejection methods 158 sources are retrieved with signal-to-noises ranging from 8-10. I have performed aperture photometry and measured proper motions for a set of candidates that were observed during the follow-up campaign. I then present a new sample of potentially white dwarfs with common proper motions main sequence star companions. The white dwarfs are retrieved from SuperCOSMOS whereas stellar companions are from Tycho. I present spectra for 39 WD candidates and for 6 stars. Temperatures and surface gravities are estimated for the white dwarf objects, whilst main sequence stars abundances are obtained from the fitting of synthetic spectra to the observations. Finally I discuss the implications of these findings and what future work can be done with these benchmark systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available