Jim Fuller edited Abstract.tex  almost 9 years ago

Commit id: 6d2a850a8f02ba5b41c386d0ac2cf69f1e7ec9d6

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%Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can suppress dipole oscillation modes. The suppression arises from a magnetic greenhouse effect trapping oscillation mode energy within the core. Suppressed dipole modes are indeed observed in a substantial fraction of \textit{Kepler} young red giants, and we interpret these as stars with magnetized cores. We place lower limits and in one case measure the value of the core field strengths, which indicate these stars have retained fossil fields or hosted a core dynamo during the main sequence. This novel technique allows for constraints on internal magnetic fields in large populations of stars.  Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can suppress dipole oscillation modes. The suppression arises from a magnetic greenhouse effect trapping oscillation mode energy within the core. Suppressed dipole modes are indeed observed in a substantial fraction of \textit{Kepler} young red giants, and we interpret these as stars with magnetized cores. We find field strengths larger than roughly $10^4 \,{\rm G}$ can account for the observed suppression suppression,  and in one case measure a core field strength of $\sim 10^7 \,{\rm G}$, indicating many red giants have retained fossil fields or hosted a core dynamo during the main sequence.