Mullard Space Science Laboratory

C. M. Bridge
A study of the accretion flow in eclipsing polars

2004 (supervisor: M. S. Cropper)

This thesis is concerned with the accretion flow in the high magnetic field cataclysmic variables known as polars. I first provide a brief introduction to the subjects discussed in this thesis, followed by an introduction to the instruments used to make the observations: the optical onservations were made usign the S-Cam 2 superconducting tunnel junction camera and X-ray observations using XMM-Newton. The chapters that follow this are concerned with two polars: HU Aqr and EP Dra. In Chapter 3, I apply an eclipse mapping technique to the optical light curves of HU Aqr to reconstruct the brightness distribution along the accretion flow. In Chapter 4 I discuss the light curves of EP Dra, a system which until now has not been well studied. The light curves of EP Dra all show variability and a unique light curve shape. Based on the observations and the eclipse mapping I make insights into the nature of the accretion flow in the two systems. Chapter 5 presents modelling of the optical light curves of HU Aqr and EP Dra using a technique based on `genetically modified fire-flies'. Unlike previous techniques to reconstruct the brightness distribution of the accretion flow, this places as few constraints on the location of the material as possible. This is the first time this technique has been applied to observed light curves. In Chapter 6 I present XMM-Newton observations of EP Dra. I use X-ray and simultaneous optical/UV observations to provide a comparison with the observations of Chapter 4, and provide further insights into the accretion flow in this system. Finally, I present model accretion flows irradiated by X-ray emission from the accretion shock. This allows the construction of accretion flow temperature profiles, the location of different ionized species along the flow, and the construction of theoretical Doppler maps.


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