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The asteroseismology of red giant stars has continued to yield surprisessince the onset of high-precision photometry from space-based observations. Anexciting new theoretical result shows that the previously observed suppressionof dipole oscillation modes in red giants can be used to detect strong magneticfields in the stellar cores. A fundamental facet of the theory is that nearlyall the mode energy leaking into the core is trapped by the magnetic greenhouseeffect. This results in clear predictions for how the mode visibility changesas a star evolves up the red giant branch, and how that depends on stellarmass, spherical degree, and mode lifetime. Here, we investigate the validity ofthese predictions with a focus on the visibility of different sphericaldegrees. We find that mode suppression weakens for higher degree modes with anaverage reduction in the quadrupole mode visibility of up to 49% for the leastevolved stars in our sample, and no detectable suppression of octupole modes,in agreement with the theoretical predictions. We furthermore find evidence forthe influence of increasing mode lifetimes on the measured visibilities alongthe red giant branch, in agreement with previous independent observations.These results support the theory that strong internal magnetic fields areresponsible for the observed suppression of non-radial modes in red giants. Wealso find preliminary evidence that stars with suppressed dipole modes onaverage have slightly lower metallicity than normal stars.

Suppression of quadrupole and octupole modes in red giants observed by Kepler