Variable Stars in the SuperWASP All-Sky Survey

Thiemann, Heidi Budd (2021). Variable Stars in the SuperWASP All-Sky Survey. PhD thesis The Open University.



The SuperWASP project has a vast archive of stellar variables still to be exploited. In this work, I explored three aspects of stellar variability using this archive: rotational variation, contact binaries, and citizen science.

In the first part of my research, I used the SuperWASP archive and ASAS-SN Catalogue of Variable Stars to identify rotationally modulated stellar variables with a coincident X-ray source. These results were used to characterise the rotation-activity relation for a sample of field stars. For the SuperWASP targets, I found a slope of the power-law fit to the unsaturated regime of $\beta = -1.84\pm0.18$, in line with the canonical value of $\beta = -2$, and evidence of the supersaturated regime.

In the second part of my research, a candidate near contact red giant eclipsing binary was discovered, thought to be the progenitor of the rare transient, red novae. I characterised 27 candidates both photometrically and spectroscopically. The observational data fed directly into component modelling and evolutionary modelling, confirming their existence and identifying component masses of $\sim$0.3--3 $M_{\odot}$, semi-major axes of $\sim$13--70 $R_{\odot}$, temperatures of $\sim$3600-5600 K, and radii of 3--25 $R_{\odot}$. For such unusual binaries to form, I identified that they must have evolved from detached binaries with mass ratios of $q$=1$\pm$0.01, and are on the brink of experiencing a rapid inspiralling event which will likely occur within just 5,000 years to 29 Myr (0.03 Gyr). It is, however, uncertain whether the death of near contact red giant eclipsing binaries will form white dwarf binaries, red novae, or something else entirely.

In the third part of my research, I analysed the results of 2 years of engagement with members of the public through \textit{SuperWASP Variable Stars}. I identified over 300 new stellar variables and laid the groundwork for future exploitation of the SuperWASP archive.

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