Heartbeat Stars and the Ringing of Tidal Pulsations

Hambleton, Kelly (2016) Heartbeat Stars and the Ringing of Tidal Pulsations. Doctoral thesis, University of Central Lancashire.

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With the advent of high precision photometry from satellites such as the Kepler satellite, a whole new collection of interesting astronomical features and objects has been revealed: heartbeat stars are prime example of this. Heartbeat stars are eccentric ellipsoidal variables that undergo strong tidal interactions at periastron, when the stars are close to each other. These interactions induce the deformation of the stars, which causes a change in the cross-sectional area and temperature variations over the stellar surface. In the precise Kepler data, these changes cause a notable variation in the light curve in the form of a tidal pulse. In this work I present novel modelling tools produced specifically to model heartbeat stars. These include the bayes-todcor software, which generates radial velocities and fundamental stellar parameters from spectra using a combination of emcee and todcor; and software created for modelling heartbeat stars, which is a combination of phoebe, emcee and my own codes. One of the features added to the phoebe modelling software is the ability to model tidally induced pulsations simultaneously with the binary star features, enabling a complete and accurate heartbeat star model to be determined. Tidally induced pulsations are stellar oscillations driven by the tidal force of the companion star. Approximately 20% of our sample of 173 Kepler heartbeat stars show prominent tidally induced pulsations, which present in the light curve as oscillations at precise multiples of the orbital frequency. In this work I present a selection of heartbeat stars, modelled with the aforementioned codes. The majority of these show tidally induced pulsations. Additional features include rapid apsidal motion, tidally resonant modes, solar-like oscillations and tidally influenced pressure modes. I also applied my codes to a binary star presenting a strong case of frequency modulation, the Doppler shift of the stellar pulsation frequencies as the pulsating star moves towards and away from the observer. Combined, these objects form the majority of heartbeat stars that have been studied in detail in the literature today.

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