EUV, X-ray and optical studies of white dwarf binary systems

This thesis describes an EUV, X-ray and optical study of white dwarfs, concentrating on those in binary systems with a late-type companion star. In the introductory chapter I outline the types of binary systems known to include white dwarf components and the observed characteristics of binary and single white dwarfs. Chapter 2 discusses WFC-discovered white dwarfs which appear isolated. I derive magnitudes and temperatures both from optical spectra and EUV data, and compare this population to that of known field white dwarfs. I also report on a search for any further 'hidden' white-dwarf/red-dwarf systems. Chapter 3 presents extensive work on RE1016-05, a white-dwarf/red-dwarf candidate pre-cataclysmic binary, discovered in the ROSAT all-sky-survey. EUV, X-ray and optical data are analysed to determine the parameters and nature of the system. In chapters 4 and 5 I describe work undertaken on other white-dwarf/red dwarf systems: several discovered with the ROSAT WFC ; and several pre-cataclysmic systems known before the all-sky-survey. EUV and X-ray observations (obtained during the ROSAT survey and pointed phases) and optical follow-up spectra are analysed to determine parameters of both components in the systems and extract information about their evolutionary state and the structure and composition of the white dwarf atmospheres. The main results and conclusions to be drawn from this thesis are summarised in chapter 6. Appendix A describes software I wrote to aid in the reduction of the large volumes of spectral data accumulated by the ROSAT Optical Identification Programme. Appendix B contains a brief description of the ROSAT spacecraft and our (MSSL) participation in the WFC survey data reduction.