Characterisation Of The Blazhko Effect In RR Lyrae Stars Using SuperWASP Data

Greer, Paul A. (2018). Characterisation Of The Blazhko Effect In RR Lyrae Stars Using SuperWASP Data. PhD thesis The Open University.



This thesis investigates the characteristics of the Blazhko effect using data from the SuperWASP archive. The SuperWASP instrument combines wide-field coverage with a short cadence, providing time-series analysis on a range of timescales for a large number of stars. The Blazhko effect is the amplitude and frequency modulation of RR Lyrae variable pulsating stars. Its physical causes are still unexplained by stellar structure and evolution models. The stellar pulsation mechanism and modulation are introduced before comparing the WASP project to other wide-field surveys.

The aim of this research is to identify correlations between the basic pulsation and Blazhko effect characteristics that may provide clues to its origins. To accomplish this, the Blazhko effect is investigated in temporal, frequency and phase spaces.

A catalogue of 4963 RRab class RR Lyrae objects was created through the classification of phase-folded light curves. Blazhko periods were calculated for 18 out of 20 highly modulated objects by phase-folding the amplitude modulation induced upper envelope function of their light curves.

983 Blazhko objects have been identified using coincident low frequency peaks and sidebands, or equidistant sidepeaks, in frequency spectra created using the CLEAN algorithm. Analysis of pulsation and Blazhko attributes within this large sample shows no correlation between them.

140 Blazhko candidates were also identified by short-term periodic trends in their O-C diagrams. This phase domain analysis also led to the identification of 17 candidates for rare binary objects, due to their sinusoidal O-C curves. 73 objects had quadratic O-C curves, suggesting binary candidates with periods longer than the duration of SuperWASP observations.

The classification and investigation of Blazhko effect and binary candidates contained herein provide the opportunity for further study with both existing, and future, ground- and space-based missions such as Gaia, the LSST and PLATO.

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