title: 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 evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, 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 surface. 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 cores, 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.
authors.affiliation: Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.|Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
authors.forename: Dennis
authors.initials: D
authors.lastname: Stello
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: Matteo
authors.initials: M
authors.lastname: Cantiello
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.|TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Fuller
authors.affiliation: Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.|Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.|SETI Institute, 189 Bernardo Avenue, Mountain View, California 94043, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Huber
authors.affiliation: Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot-IRFU/SAp Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France.
authors.forename: Rafael A
authors.initials: RA
authors.lastname: García
authors.affiliation: Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.|Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Bedding
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.|Department of Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: Lars
authors.initials: L
authors.lastname: Bildsten
authors.affiliation: Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
authors.forename: Victor Silva
authors.initials: VS
authors.lastname: Aguirre