Travis MetcalfeSpace Science Institute +

Stellar Astrophysics Centre

Asteroseismic Signatures of Magnetic Activity Variations in Solar-type Stars

Collaborators: W.A. Dziembowski, P.G. Judge, M. Snow, C. Karoff, W.J. Chaplin, R. Garcia, S. Mathur, D. Salabert

Goldreich et al. (1991)

• Magnetic perturbations modify the near-surface propagation speed

• Also leads to decreased convective velocity and change in temperature

• Secondary effects are required to explain the solar f-mode behavior

Metcalfe et al. (2007)

• Parameterize shifts with ~ A0 (R / M) Qj(Dc) and fit MDI p-mode data

• A0 ~ activity level, while the depth of the source Dc ~ Hp ~ L1/4 R3/2 / M

• Normalizing shifts by parametrization mostly removes dependencies

Metcalfe et al. (2007)

Chaplin et al. (2007)

Salabert et al. (2011)

Mathur et al. (in prep.)

Overview

• Over the stellar cycle, magnetic activity induces shifts in the oscillation frequencies and reduces oscillation amplitudes by inhibiting convection.

• The first detection of both effects in CoRoT data supports the relation proposed by Dziembowski, with larger than solar shifts in a hotter star.

• The shortest cycles and the largest frequency shifts are expected in F stars, making them ideal targets for probing stellar activity with Kepler.