Modeling the Rise of Fibril Magnetic Fields in Fully Convective Stars

Abstract

Many fully convective stars exhibit a wide variety of surface magnetism, including starspots and chromospheric activity. The manner by which bundles of magnetic field traverse portions of the convection zone to emerge at the stellar surface is not especially well understood. In the Solar context, some insight into this process has been gleaned by regarding the magnetism as consisting partly of idealized thin flux tubes (TFT). Here, we present the results of a large set of TFT simulations in a rotating spherical domain of convective flows representative of a 0.3 solar-mass, main-sequence star. This is the first study to investigate how individual flux tubes in such a star might rise under the combined influence of buoyancy, convection, and differential rotation. A time-dependent hydrodynamic convective flow field, taken from separate 3D simulations calculated with the anelastic equations, impacts the flux tube as it rises. Convective motions modulate the shape of the initially buoyant flux ring, promoting localized rising loops. Flux tubes in fully convective stars have a tendency to rise nearly parallel to the rotation axis. However, the presence of strong differential rotation allows some initially low latitude flux tubes of moderate strength to develop rising loops that emerge in the near-equatorial region. Magnetic pumping suppresses the global rise of the flux tube most efficiently in the deeper interior and at lower latitudes. The results of these simulations aim to provide a link between dynamo-generated magnetic fields, fluid motions, and observations of starspots for fully convective stars.

20 pages, 15 figures, accepted to Astrophysical Journal

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• Mapping stellar surfaces II: An interpretable Gaussian process model for light curves
• Giant white-light flares on fully convective stars occur at high latitudes
• The Radius and Entropy of a Magnetized, Rotating Fully-convective Star: Analysis With Depth-dependent Mixing Length Theories
• Connecting the large- and the small-scale magnetic fields of solar-like stars
• Longitudinally Modulated Dynamo Action in Simulated M-Dwarf Stars
• Flux-tubes forming instability near the base of the rotating convection zone: A possible explanation for low latitudes of sunspots
• Theoretical and Observational Evidence for Coriolis Effects in Coronal Magnetic Fields Via Direct Current Driven Flaring Events
• The corona of a fully convective star with a near-polar flare
• Flaring Latitudes in Ensembles of Low Mass Stars
• On the Description of Transverse Wave Propagation Along Thin Magnetic Flux Tubes
• The Suppression and Promotion of Magnetic Flux Emergence in Fully Convective Stars
• Dynamo Processes Constrained by Solar and Stellar Observations
• Thermomagnetic Ettingshausen-Nernst effect in tachocline, magnetic reconnection phenomenon in lower layers, axion mechanism of solar luminosity variations, coronal heating problem solution and mechanism of ADM variations around BH