Suppression of Quadrupole and Octupole Modes in Red Giants Observed by Kepler
Abstract
An exciting new theoretical result shows that observing suppression of dipole oscillation modes in red giant stars can be used to detect strong magnetic fields in the stellar cores. A fundamental facet of the theory is that nearly all the mode energy leaking into the core is trapped by the magnetic greenhouse effect. This results in clear predictions for how the mode visibility changes as a star evolves up the red giant branch, and how that depends on stellar mass, spherical degree, and mode lifetime. Here, we investigate the validity of these predictions with a focus on the visibility of different spherical degrees. We find that mode suppression weakens for higher degree modes with a reduction in the quadrupole mode visibility of up to 49%, and no detectable suppression of octupole modes, in agreement with theory. We find evidence for the influence of increasing mode lifetimes on the visibilities along the red giant branch, in agreement with previous independent observations. These results support the theory that strong internal magnetic fields cause suppression of non-radial modes in red giants. We also find preliminary evidence that stars with suppressed dipole modes on average have slightly lower metallicity than normal stars.
Additional Information
© 2016 Astronomical Society of Australia. Received January 19 2016; Accepted February 12 2016. We acknowledge the entire Kepler team, whose efforts made these results possible. D.S. is the recipient of an Australian Research Council Future Fellowship (project number FT140100147). J.F. acknowledges support from NSF under grant no. AST-1205732 and through a Lee DuBridge Fellowship at Caltech. R.A.G. acknowledge the support of the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 269194 (IRSES/ASK), the ANR- IDEE (n ANR-12-BS05-0008), and from the CNES. D.H. acknowledges support by the Australian Research Council's Discovery Projects funding scheme (project number DE140101364) and support by the National Aeronautics and Space Administration under Grant NNX14AB92G issued through the Kepler Participating Scientist Program. This project was supported by NASA under TCAN grant number NNX14AB53G, and the NSF under grants PHY 11-25915 and AST 11-09174. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (Grant agreement no.: 267864).Attached Files
Submitted - 1602.05193v1.pdf
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Additional details
- Eprint ID
- 66033
- Resolver ID
- CaltechAUTHORS:20160408-143954572
- FT140100147
- Australian Research Council
- AST-1205732
- NSF
- Lee A. DuBridge Foundation
- 269194
- European Research Council (ERC)
- ANR-12-BS05-0008
- Agence Nationale pour la Recherche (ANR)
- Centre National d'Études Spatiales (CNES)
- DE140101364
- Australian Research Council
- NNX14AB92G
- NASA
- NNX14AB53G
- NASA
- PHY 11-25915
- NSF
- AST 11-09174
- NSF
- DNRF106
- Danish National Research Foundation
- 267864 ASTERISK
- European Research Council (ERC)
- Created
-
2016-04-12Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field
- Caltech groups
- TAPIR, Walter Burke Institute for Theoretical Physics