Magnetic Oscillations in Stars

Some stars contain magnetic fields which we can observe in the spectrum by the Zeeman effect. These fields can be very strong: around 10kG which is around 20,000 times stronger than the Earth's magnetic field. However, since we only observe the surface of the star, it is difficult to say what the structure of the field should be in the interior. Curiously, a few of these stars appear to display periodic oscillations in their rotation periods, i.e. they are spinning up and slowing down over timescales of order a decade. This phenomenon is likely to be magnetic oscillations, that is, standing magnetic waves permeating the entire star. In this project, the student will perform simulations of a magnetic star undergoing oscillations, investigating what kinds of oscillations are possible, how their frequencies are related, and what the observations can tell us about the geometry of these magnetic fields in the stellar interior. In addition, in the growing field of asteroseismology higher frequency modes are observed in some stars; these oscillations are essentially acoustic in nature but the frequencies are affected by magnetic fields. This project will therefore help asteroseismologists probe the internal structure and rotation of stars. Further reading: http://arxiv.org/abs/1110.1104/. Please contact Dr. Braithwaite (jonathan-at-astro.uni-bonn.de) for more information.

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