Even though accretion and binary star interaction is a well-studied topic, we understand preciously little of the physics of the interaction and the mechanism through which angular momentum is transferred in the system. CVs are the ideal test population to study these effects, as they are nearby, bright, and plentiful enough to do population studies on. I have worked on a large project to characterise the faint CVs found in the Catalina Real-time Transient Survey (CRTS) and am extending this work to detemine a reliable space density estimate of these accreting binaries that can be used as direct input to theoretical models of binary evolution. A particular interest at the moment are the AMCVn stars - they are rare, ultra-compact helium accreting binaries of which only ~55 are known so far. They have orbital periods that are typically shorter than an hour!

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Such short period binaries, along with others that display eclipses, stellar pulsations, spinning white dwarfs etc. display variability on second- or sub-second timescales. I am part of the team based at the Universities of Warwick and Sheffield, who operate and run the triple-beam ultra-fast camera ULTRACAM as a visitor instrument on a variety of telescopes (WHT, NTT, VLT). It allows up to observe these phenomena with high time resolution and simultaneously in three colours, which can tell us a lot about the physics and/or geometry of these systems.