CCD Time-Series Photometry of White Dwarf Stars
This thesis describes a practical programme that focused on CCD photometry of pulsating white dwarf (WD) stars. The first part of this thesis describes the development of two high-speed CCD photometer instruments and their data reduction pipeline, while the remainder describes the observation and analysis of several pulsating WDs and other targets. The two photometers (Puoko-nui North and South) share a common hardware design that is optimized for acquiring efficient photometry with integration periods of milliseconds through to minutes. The design integrates a commercial CCD (Charge-Coupled Device) camera and GPS (Global Positioning System) receiver with custom timing electronics and control software. The reduction and visualization software developed for these instruments provide detailed real-time information to the observer, and a streamlined data reduction pipeline. EC04207-4748 is a pulsating helium atmosphere WD that shows significant non-sinusoidal intensity variations. We show that the pulsation spectrum of this WD can be described by four independent pulsation eigenmodes plus linear combinations that arise from non-linear energy transport through a sub-surface convection layer. Our results are consistent with similar analyses that have been made for similar stars, and add an additional data point to the growing catalogue of these convection measurements. We argue that the convection layer depth may form a useful substitute for the effective temperatures of these WDs. GWLibrae is the class prototype of the accreting WD pulsators. These stars exist in cataclysmic variable (CV) systems, and show a mix of CV and pulsating WD-related phenomena. Our observations of GW Librae four - six years after its 2007 outburst show signs of quasi-stable intensity modulations that we believe may be caused by non-radial pulsations, but these are not convincingly explained by existing WD or CV models. L19-2 is a hydrogen atmosphere WD pulsator that shows extremely stable pulsation behaviour. We combine new observations with archival observations dating back to the mid 1970's, and derive a preliminary estimate of the period rate of change Ṗ for two of the pulsation modes in this target. We show a clear result for the main 192 s pulsation mode Ṗf₂ ≾ 10⁻¹⁴ s s-¹, and discuss the improvements that we plan to make in order to convincingly improve this constraint by an additional order of magnitude. Observations of other rapidly variable targets include two extremely low mass (ELM) WDs, which exhibit variability due to their orbital motion (J0751) as well as non-radial pulsations (J1518); the 33 ms optical period of the Crab Pulsar; the helium atmosphere WD pulsators EC05221-4725 and EC20058-5234; the stable hydrogen atmosphere pulsator G117–B15A; and the eclipsing sdB binary system PG1336-018.