Seismology of the Surface Layers of Stars

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My research is primarily directed toward understanding how stars work by analyzing the harmonic structure of sound waves that bounce around their interiors. The sound waves are not heard but seen. As a sound wave travels through the interior of a star it causes the material of the star to oscillate up and down into warmer and cooler regions of the star. The changes in temperature of the material can be seen on the surface of a star as minute variations in the star's brightness. From the brightness fluctuations, we can deduce the frequency and amplitudes of the sound waves, which, in turn, can be used to build a picture of what is going on inside the star. In order to clearly see the fluctuations we need to observe the same star continuously for weeks to months, without interruption from weather and daylight. In addition, we need to avoid the twinkling effects of the earth's atmosphere. Therefore, we must observe from a "space telescope" specifically designed to observe tiny variations in light. Canadian scientists were the first to build and launch (June 30, 2003) such a satellite, called MOST (Microvariability and Oscillations on STars). Since then two additional satellites, CoRoT (French Space Agency CNES) and Kepler (NASA) have been deployed. My research colleagues, students and I are analyzing the data obtained from these satellites to build a detailed picture of the interiors stars. I am primarily interested in untangling the effects that the surface layers have on a star's oscillation spectrum. All oscillation spectra are affected by the surface layers since the sound waves must pass through this layer in their journey through the star. The surface layers introduce some of most difficult-to-model physics including convection, rotation, and magnetic fields. I will model the physics and I will develop strategies to isolate the effects that the surface layer physics have on the oscillation spectrum so that I can test my models.