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A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars

Abstract

Magnetic fields play a part in almost all stages of stellar evolution1. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes2,3. Intermediate-mass stars do not have deep convective envelopes4, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process5. These stars do have convective cores that might produce internal magnetic fields6, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface7. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores8, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6–2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.

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Figure 1: Oscillation spectra of six red giants observed with Kepler.
Figure 2: Visibility of dipolar modes for red giants observed with Kepler.
Figure 3: Observed fraction of stars with suppressed dipolar modes.
Figure 4: Critical magnetic field strength required to suppress dipole mode oscillations.

References

  1. Landstreet, J. D. Magnetic fields at the surfaces of stars. Astron. Astrophys. Rev. 4, 35–77 (1992)

    ADS  Article  Google Scholar 

  2. Parker, E. N. Hydromagnetic dynamo models. Astrophys. J. 122, 293–314 (1955)

    ADS  MathSciNet  Article  Google Scholar 

  3. Donati, J.-F. & Landstreet, J. Magnetic fields of nondegenerate stars. Annu. Rev. Astron. Astrophys. 47, 333–370 (2009)

    CAS  ADS  Article  Google Scholar 

  4. Kippenhahn, R. & Weigert, A. Stellar Structure and Evolution (Springer, 1990)

  5. Power, J., Wade, G. A., Aurière, M., Silvester, J. & Hanes, D. Properties of a volume-limited sample of Ap-stars. Contrib. Astron. Observ. Skalnate Pleso 38, 443–444 (2008)

    ADS  Google Scholar 

  6. Brun, A. S., Browning, M. K. & Toomre, J. Simulations of core convection in rotating A-type stars: magnetic dynamo action. Astrophys. J. 629, 461–481 (2005)

    ADS  Article  Google Scholar 

  7. Aurière, M. et al. The magnetic fields at the surface of active single G-K giants. Astron. Astrophys. 574, A90 (2015)

    Article  Google Scholar 

  8. Fuller, J., Cantiello, M., Stello, D., Garcia, R. A. & Bildsten, L. Strong internal magnetic fields explain suppressed oscillation modes in red giant stars. Science 350, 423–426 (2015)

    CAS  ADS  MathSciNet  Article  Google Scholar 

  9. De Ridder, J. D. et al. Non-radial oscillation modes with long lifetimes in giant stars. Nature 459, 398–400 (2009)

    CAS  ADS  Article  Google Scholar 

  10. Stello, D., Bruntt, H., Preston, H. & Buzasi, D. Oscillating K giants with the WIRE satellite: determination of their asteroseismic masses. Astrophys. J. 674, L53–L56 (2008)

    ADS  Article  Google Scholar 

  11. García, R. A. & Stello, D. in Extraterrestrial Seismology (eds Tong, V. C. H. & García, R. A. ) Ch. 11 (Cambridge Univ. Press, 2015)

  12. Bedding, T. R. et al. Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars. Nature 471, 608–611 (2011)

    CAS  ADS  Article  Google Scholar 

  13. Stello, D. et al. Asteroseismic classification of stellar populations among 13,000 red giants observed by Kepler. Astrophys. J. 765, L41 (2013)

    ADS  Article  Google Scholar 

  14. Mosser, B. et al. Mixed modes in red giants: a window on stellar evolution. Astron. Astrophys. 572, L5 (2014)

    ADS  Article  Google Scholar 

  15. Beck, P. G. et al. Kepler detected gravity-mode period spacings in a red giant star. Science 332, 205 (2011)

    CAS  ADS  Article  Google Scholar 

  16. Mosser, B. et al. Spin down of the core rotation in red giants. Astron. Astrophys. 548, A10 (2012)

    Article  Google Scholar 

  17. Dupret, M.-A. et al. Theoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giants. Astron. Astrophys. 506, 57–67 (2009)

    ADS  Article  Google Scholar 

  18. Mosser, B. et al. Characterization of the power excess of solar-like oscillations in red giants with Kepler. Astron. Astrophys. 537, A30 (2012)

    Article  Google Scholar 

  19. García, R. A. et al. Study of KIC 8561221 observed by Kepler: an early red giant showing depressed dipolar modes. Astron. Astrophys. 563, A84 (2014)

    Article  Google Scholar 

  20. Gough, D. O. & McIntyre, M. E. Inevitability of a magnetic field in the Sun’s radiative interior. Nature 394, 755–757 (1998)

    CAS  ADS  Article  Google Scholar 

  21. Braithwaite, J. & Spruit, H. C. A fossil origin for the magnetic field in A stars and white dwarfs. Nature 431, 819–821 (2004)

    CAS  ADS  Article  Google Scholar 

  22. Duez, V., Braithwaite, J. & Mathis, S. On the stability of non-force-free magnetic equilibria in stars. Astrophys. J. 724, L34–L38 (2010)

    ADS  Article  Google Scholar 

  23. Moss, D. On the magnetic flux distribution in magnetic CP stars. Mon. Not. R. Astron. Soc. 226, 297–307 (1987)

    ADS  Article  Google Scholar 

  24. Cantiello, M., Mankovich, C., Bildsten, L., Christensen-Dalsgaard, J. & Paxton, B. Angular momentum transport within evolved low-mass stars. Astrophys. J. 788, 93 (2014)

    ADS  Article  Google Scholar 

  25. Busso, M., Wasserburg, G. J., Nollett, K. M. & Calandra, A. Can extra mixing in RGB and AGB stars be attributed to magnetic mechanisms? Astrophys. J. 671, 802–810 (2007)

    CAS  ADS  Article  Google Scholar 

  26. Nucci, M. C. & Busso, M. Magnetohydrodynamics and deep mixing in evolved stars. I. Two- and three-dimensional analytical models for the asymptotic giant branch. Astrophys. J. 787, 141 (2014)

    ADS  Article  Google Scholar 

  27. Salaris, M. & Cassisi, S. Evolution of Stars and Stellar Populations (John Wiley & Sons, 2005)

  28. Miglio, A. et al. Asteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819. Mon. Not. R. Astron. Soc. 419, 2077–2088 (2012)

    ADS  Article  Google Scholar 

  29. Corsaro, E., Ridder, J. D. & Garcia, R. A. Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler. Astron. Astrophys. 579, A83 (2015)

    Article  Google Scholar 

  30. Huber, D. et al. Asteroseismology of red giants from the first four months of Kepler data: global oscillation parameters for 800 stars. Astrophys. J. 723, 1607–1617 (2010)

    CAS  ADS  Article  Google Scholar 

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Acknowledgements

This paper has been written collaboratively, on the web, using Authorea (http://www.authorea.com). 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 number AST-1205732 and through a Lee DuBridge Fellowship at Caltech. R.A.G. acknowledges the support of the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement number 269194 (IRSES/ASK), the CNES, and the ANR-12-BS05-0008, IDEE. 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 number NNX14AB92G issued through the Kepler Participating Scientist Program. This project was supported by NASA under TCAN grant number NNX14AB53G, and by the NSF under grant numbers PHY11-25915 and AST11-09174. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (grant agreement number DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (grant agreement number 267864).

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Contributions

D.S. measured and interpreted mode visibilities; M.C. and J.F. calculated and interpreted theoretical models; D.H. and D.S. calculated power spectra and measured large frequency separations; R.A.G., T.R.B., L.B. and V.S.A. contributed to the discussion of the results. All authors commented on the manuscript.

Corresponding author

Correspondence to Dennis Stello.

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Stello, D., Cantiello, M., Fuller, J. et al. A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars. Nature 529, 364–367 (2016). https://doi.org/10.1038/nature16171

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