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Asteroseismology of magnetised, rotating red giant stars

Shyeh Tjing Loi (University of Cambridge) // June 17, 2021

Abstract: It is thought that magnetic fields must be present in the interiors of stars to resolve certain discrepancies between theory and observation, but such fields are difficult to detect and characterise. Asteroseismology is a powerful technique for inferring the internal structures of stars by measuring their oscillation frequencies, and succeeds particularly with evolved stars, owing to their mixed modes, which are sensitive to the deep interior. In this talk I will present the results of a phenomenological study of the combined effects of rotation and magnetism on the seismic properties of evolved stars, focusing on the regime where Coriolis and Lorentz forces are comparable, and weak enough that first-order perturbation theory applies. Axisymmetric “twisted-torus” field configurations are used, which are allowed to be misaligned with respect to the rotation axis. Factors such as the field radius, topology and obliquity are examined. The interplay of rotation and magnetism is shown to be complex: for example, nearly symmetric multiplets of apparently low multiplicity can arise even under a substantial field, suggesting the need for proper modelling of rotation and magnetism simultaneously in order to draw robust conclusions about interior properties. I will also discuss the distinctive signatures of magnetic splitting that may allow it to be disentangled from rotational splitting, which may impact future strategies for seismic interpretation of these objects.

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