1 research outputs found
Simulations of dynamo action in fully convective stars
We present three-dimensional nonlinear magnetohydrodynamic simulations of the
interiors of fully convective M-dwarfs. Our models consider 0.3 solar-mass
stars using the Anelastic Spherical Harmonic code, with the spherical
computational domain extending from 0.08-0.96 times the overall stellar radius.
Like previous authors, we find that fully convective stars can generate
kG-strength magnetic fields (in rough equipartition with the convective flows)
without the aid of a tachocline of shear. Although our model stars are
everywhere unstably stratified, the amplitudes and typical pattern sizes of the
convective flows vary strongly with radius, with the outer regions of the stars
hosting vigorous convection and field amplification while the deep interiors
are more quiescent. Modest differential rotation is established in hydrodynamic
calculations, but -- unlike in some prior work --strongly quenched in MHD
simulations because of the Maxwell stresses exerted by the dynamo-generated
magnetic fields. Despite the lack of strong differential rotation, the magnetic
fields realized in the simulations possess significant mean (axisymmetric)
components, which we attribute partly to the strong influence of rotation upon
the slowly overturning flows.Comment: Accepted to the ApJ. 20 pages (emulateapj), 4 color figures
compressed to low-resolution; higher-resolution equivalents are available at
http://lcd-www.colorado.edu/~brownim/browning_2007_mstars.pd