Asteroseismology can reveal strong internal magnetic fields in red giant 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 be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, arising from a magnetic greenhouse effect that scatters and traps oscillation-mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes, which we interpret as stars with strongly magnetized cores. We find that field strengths larger than ~10^5 gauss may produce the observed depression, and in one case we infer a minimum core field strength of ≈10^7 gauss.
© 2015 American Association for the Advancement of Science. Received for publication 29 May 2015. Accepted for publication 15 September 2015. The authors of this paper thank the Kavli Institute for Theoretical Physics and the organizers of the Galactic Archaeology and Precision Stellar Astrophysics program held from January to April 2015. J.F. acknowledges partial support from NSF under grant no. AST-1205732 and through a Lee DuBridge Fellowship at the California Instiute of Technology. R.A.G. acknowledge the support of the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312844 (SPACEINN), and from the Centre National d'Études Spatiales. D.S. acknowledges support from the Australian Research Council. This project was supported by NASA under Theory and Computational Astrophysics Network grant no. NNX14AB53G and NSF under grants PHY 11-25915 and AST 11-09174.
Supplemental Material - Fuller.SM.pdf