Star-in-a-box simulations of fully convective stars

Abstract

(abridged) Context: Main-sequence late-type stars with masses less than $0.35M_{\odot }$ are fully convective. Aims: The goal is to study convection, differential rotation, and dynamos as functions of rotation in fully convective stars. Methods: Three-dimensional hydrodynamic and magnetohydrodynamic numerical simulations with a star-in-a-box model, where a spherical star is immersed inside of a Cartesian cube, are used. The model corresponds to a $0.2M_{\odot }$ M5 dwarf. Rotation periods ($P_{\mathrm{rot}}$) between 4.3 and 430 days are explored. Results: The slowly rotating model with $P_{\mathrm{rot}}=430$ days produces anti-solar differential rotation with a slow equator and fast poles, along with predominantly axisymmetric quasi-steady large-scale magnetic fields. For intermediate rotation ($P_{\mathrm{rot}}=144$ and $43$ days) differential rotation is solar-like (fast equator, slow poles) and large-scale magnetic fields are mostly axisymmetric and either quasi-stationary or cyclic. The latter occurs in a similar parameter regime as in other numerical studies in spherical shells, and the cycle period is similar to observed cycles in fully convective stars with comparable $P_{\mathrm{rot}}$. In the rapid rotation regime the differential rotation is weak and the large-scale magnetic fields are increasingly non-axisymmetric with a dominating $m=1$ mode. This large-scale non-axisymmetric field also exhibits azimuthal dynamo waves. Conclusions: The results of the star-in-a-box models agree with simulations of partially convective late-type stars in spherical shells in that the transitions in differential rotation and dynamo regimes occur at similar rotational regimes in terms of the Coriolis (inverse Rossby) number. This similarity between partially and fully convective stars suggests that the processes generating differential rotation and large-scale magnetism are insensitive to the geometry of the star.

17 pages, 11 figures, submitted to Astron. Astrophys, revised as per referee report

References in corpus (25)

• Large-scale magnetic topologies of late M dwarfs
• The case for a distributed solar dynamo shaped by near-surface shear
• Simulations of dynamo action in fully convective stars
• Large-scale magnetic topologies of early M dwarfs
• Magnetic field generation in fully convective rotating spheres
• Mean-field concept and direct numerical simulations of rotating magnetoconvection and the geodynamo
• Persistent Magnetic Wreaths in a Rapidly Rotating Sun
• Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• Solar-type dynamo behaviour in fully convective stars without a tachocline
• The Pencil Code, a modular MPI code for partial differential equations and particles: multipurpose and multiuser-maintained
• A simulation of convective dynamo in the solar convective envelope: maintenance of the solar-like differential rotation and emerging flux
• Magnetic fields of M dwarfs
• Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri
• High-resolution calculation of the solar global convection with the reduced speed of sound technique: II. Near surface shear layer with the rotation
• Calibration of the Mixing-Length Theory for Convective White Dwarf Envelopes
• Magnetic cycles in a dynamo simulation of fully convective M-star Proxima Centauri
• Formation of starspots in self-consistent global dynamo models: Polar spots on cool stars
• The large-scale magnetic field of Proxima Centauri near activity maximum
• Solar dynamo models with alpha-effect and turbulent pumping from local 3D convection calculations
• Gaia Gaps and the Physics of Low-Mass Stars. I. The Fully Convective Boundary
• Convective velocity suppression via the enhancement of subadiabatic layer: Role of the effective Prandtl number
• Single-hemisphere dynamos in M-dwarf stars
• Nonlinear regimes in mean-field full-sphere dynamo
• Activity-rotation in the dM4 star Gl 729. A possible chromospheric cycle

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