Observations of compact binary systems

In this thesis I study compact binary systems containing white dwarfs, looking at both detached systems and those that are accreting. These systems are representative of a diverse set of white dwarf binaries in the Galaxy, from which thermonuclear supernovae and other varieties of exotic stellar object emerge. Following a description of the observational techniques and data sources used, I begin with a study of a sample of white dwarfs that show evidence for excess infrared emission in their spectral energy distributions. The targets formed a subset of a larger sample after removal of systems resolved from the Hubble Space Telescope (HST). The period distribution ranges from 0.141 to 9.16 d and peaks near 0.6 d. The original sample therefore contains two sets of binaries, wide orbits (≈ 100 − 1000 au) and close orbits (. 1 − 10 au), with no systems found in the ≈ 10 − 100 au range. This observational evidence confirms the bimodal distribution predicted by population models and is also similar to results obtained in previous studies. I find no binary periods in the months to years range, supporting the post common envelope evolution scenario. The work on detached systems revealed the remarkable utility of modern wide-field photometric surveys. These are revealing rare and unusual types of white dwarf binary systems previously missed through faintness and inconspicuous photometric behaviour. I look at examples of these in the following three chapters. Chapter 4 presents a study of V1460 Her, a star only identified as an accreting binary following a rare, low amplitude outburst. V1460 Her is revealed as a remarkable system, which hosts a donor star far from thermal equilibrium, the remnant of a phase of rapid mass loss. In addition, its white dwarf shows a strong coherent signal on a period of 39 seconds in HST ultraviolet data. It shares these two aspects with the hitherto unique system AE Aqr which also has a rapidly spinning white dwarf, but, unlike V1460 Her, is propelling accreting matter out of the system altogether. Chapters 5 and 6 present new observations on magnetic CVs. V808 Aur is a polar is undergoing changes in its orbital period as is shown through ten years of photometric observations. I also derive masses for both components in the system and determine the spectral type of the donor. CRTS J215256.1+191658 is a newly discovered 3.9 hr period polar. I present high speed photometry showing the eclipse in both a high and low state and Doppler maps of the emission features revealing the flow of the accretion stream through the system.