Localizing flares to understand stellar magnetic fields and space weather in exo‐systems

I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including the following: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research.

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Observing and Modelling Stellar Magnetic Fields

EAS Publications Series ◽

10.1051/eas/0939001 ◽

2009 ◽

Vol 39 ◽

pp. 1-20 ◽

Cited By ~ 7

Author(s):

J.D. Landstreet

Keyword(s):

Magnetic Fields ◽

Stellar Magnetic Fields

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Global MHD phenomena and their importance for stellar surfaces

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015146 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 141-147

Author(s):

Rainer Arlt

Keyword(s):

Magnetic Fields ◽

Mean Field ◽

Momentum Equation ◽

Small Scale ◽

Dynamo Action ◽

Complex Activity ◽

Mhd Instabilities ◽

Stellar Magnetic Fields ◽

Mean Field Dynamo

AbstractThis review is an attempt to elucidate MHD phenomena relevant for stellar magnetic fields. The full MHD treatment of a star is a problem which is numerically too demanding. Mean-field dynamo models use an approximation of the dynamo action from the small-scale motions and deliver global magnetic modes which can be cyclic, stationary, axisymmetric, and non-axisymmetric. Due to the lack of a momentum equation, MHD instabilities are not visible in this picture. However, magnetic instabilities must set in as a result of growing magnetic fields and/or buoyancy. Instabilities deliver new timescales, saturation limits and topologies to the system probably providing a key to the complex activity features observed on stars.

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The macrodynamics of α-effect dynamos in rotating fluids

Journal of Fluid Mechanics ◽

10.1017/s0022112075000390 ◽

1975 ◽

Vol 67 (3) ◽

pp. 417-443 ◽

Cited By ~ 140

Author(s):

W. V. R. Maekus ◽

M. R. E. Proctor

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Magnetic Energy ◽

Finite Amplitude ◽

Small Scale ◽

Past Study ◽

Ohmic Loss ◽

General Will ◽

Rotating Systems ◽

Stellar Magnetic Fields

Past study of the large-scale consequences of forced small-scale motions in electrically conducting fluids has led to the ‘α-effect’ dynamos. Various linear kinematic aspects of these dynamos have been explored, suggesting their value in the interpretation of observed planetary and stellar magnetic fields. However, large-scale magnetic fields with global boundary conditions can not be force free and in general will cause large-scale motions as they grow. I n this paper the finite amplitude behaviour of global magnetic fields and the large-scale flows induced by them in rotating systems is investigated. In general, viscous and ohmic dissipative mechanisms both play a role in determining the amplitude and structure of the flows and magnetic fields which evolve. In circumstances where ohmic loss is the principal dissipation, it is found that determination of a geo- strophic flow is an essential part of the solution of the basic stability problem. Nonlinear aspects of the theory include flow amplitudes which are independent of the rotation and a total magnetic energy which is directly proportional to the rotation. Constant a is the simplest example exhibiting the various dynamic balances of this stabilizing mechanism for planetary dynamos. A detailed analysis is made for this case to determine the initial equilibrium of fields and flows in a rotating sphere.

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