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Magnetic fields at stellar surfaces are routinely observed through their Zeeman spectral signature \citep{Landstreet_1992}. A star's magnetic flux can be inherited from the gas cloud from which the star is formed, or generated by a dynamo \citep{Brandenburg_2005}. A fraction of 5-10\% of main sequence A stars is observed to have large scale, predominantly dipolar magnetic fields with amplitudes in the range 0.3-30kG (Ap stars, see e.g. \citealt{Auri_re_2007}). Surface magnetic fields have also been detected in a handful of evolved red giant stars \citep{Auri_re_2015}. In Ap stars, the fields show little or no time evolution, which together with the existence of stable magnetic configurations \citep{Braithwaite_2004,Duez_2010} supports the notion that they are not generated by a contemporary magnetic dynamo but rather inherited from the star formation phase (fossil fields).   After exhausting hydrogen in their cores, most main sequence stars evolve to become red giants. During this phase, the stellar structure is characterized by an expanding convective envelope and a contracting radiative core. Acoustic waves (p modes) in the envelope can couple to gravity waves (g modes) in the core. Consequently, non-radial stellar oscillation modes become mixed modes that contain significant inertia in probe  both the envelope (the p mode cavity) and the core (the g mode cavity). % Acoustic waves excited by turbulent convection in the envelope can propagate through the star and be used to %probe the stellar interiors. Asteroseismology of thousands of red giants has just become possible thanks to the %space satellites CoRoT and Kepler. During the red giant branch (RGB) the frequency of stochastically generated %acoustic waves (p-modes) becomes comparable to the frequency of internal gravity waves (g-modes) in the radiative %core of the star. In this situation a crosstalk between p-modes and g-modes becomes possible if enough energy can %leak through the evanescent region, which is located between the acoustic cavity and the gravity-waves cavity and %which extent depends on the harmonic degree ($\ell$) of the mode.  %This gives rise to standing waves with a mixed nature (mixed modes). The restoring force for these waves is the %pressure gradient in the envelope and gravity in the core.