scholarly journals Equilibrium solutions of relativistic rotating stars with mixed poloidal and toroidal magnetic fields

2014 ◽  
Vol 90 (10) ◽  
Author(s):  
Kōji Uryū ◽  
Eric Gourgoulhon ◽  
Charalampos M. Markakis ◽  
Kotaro Fujisawa ◽  
Antonios Tsokaros ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Rotating Stars ◽  
Equilibrium Solutions

scholarly journals Magnetic Fields in Rapidly Rotating Stars

1973 ◽  
Vol 162 (3) ◽  
pp. 289-293
Author(s):  
M. Maheswaran ◽  
H. A. B. M. de Silva
Keyword(s):  
Magnetic Fields ◽  
Rotating Stars ◽  
Rapidly Rotating Stars

scholarly journals Some travels in the land of nonlinear convection and magnetism

2019 ◽  
Vol 82 ◽  
pp. 273-294
Author(s):  
J. Toomre
Keyword(s):  
Magnetic Fields ◽  
Turbulent Convection ◽  
Rotating Stars ◽  
Dynamo Action ◽  
Penetrative Convection ◽  
Nonlinear Convection ◽  
Horizontal Structure ◽  
Solar Convection ◽  
Jean Paul ◽  
Anelastic Equations

Rotating stars with convection zones are the great builders of magnetism in our universe. Seeking to understand how turbulent convection actually operates, and so too the dynamo action that it can achieve, has advanced through distinctive stages in which Jean-Paul Zahn was often a central player, or joined by his former students. Some of the opening steps in dealing with the basic nonlinearity in such dynamics involved modal equations (with specified horizontal structure) to study convective amplitudes and heat transports achieved as solutions equilibrated by feeding back on the mean stratification. These dealt in turn with laboratory convection, with penetrative convection in Boussinesq settings, then with compressible penetration via anelastic equations in simple geometries, and finally with stellar penetrative convection in A-type stars that coupled two convection zones. Advances in computation power allowed 2-D fully compressible simulations, and then 3-D modeling including rotation, to revisit some of these convection and penetration settings within planar layers. With externally imposed magnetic fields threading the 2-D layers, magnetoconvection could then be studied to see how the flows concentrated the fields into complex sheets, or how new classes of traveling waves could result. The era of considering turbulent convection in rotating spherical shells had also arrived, using 3-D MHD codes such as ASH to evaluate how the solar differential rotation is achieved and maintained. Similarly the manner in which global magnetic fields could be built by dynamo action within the solar convection zone took center stage, finding that coherent wreaths of strong magnetism could be built, and also cycling solutions with field reversals. The coupling of convection and magnetism continues as a vibrant research subject. It is also clear that stars like the Sun do not give up their dynamical mysteries readily when highly turbulent systems are at play.

Magnetic Fields in Slowly Rotating Stars

1968 ◽  
Vol 1 (3) ◽  
pp. 89-89
Author(s):  
G.F. Davies
Keyword(s):  
Magnetic Field ◽  
Thermal Equilibrium ◽  
Meridional Circulation ◽  
Rotating Stars ◽  
Axially Symmetric ◽  
Equilibrium Solutions ◽  
Azimuthal Component ◽  
Special Cases ◽  
Field Lines ◽  
Rotating Star

Those solutions which have so far been obtained to the problem of a star with both rotation and a magnetic field have been for certain special cases, mostly time-independent. It is known that, except for stars with special rotation laws, a rotating star in hydrostatic equilibrium cannot maintain thermal equilibrium without generating slow meridional circulation of matter. It is also known that an axially symmetric field with no azimuthal component tends very strongly to keep the star in a state of isorotation, with the angular velocity constant along field lines. A magnetic field also tends to upset thermal equilibrium and produce meridional circulation. In the absence of rotation, an equilibrium poloidal field has recently been found for which there is no circulation. The present paper reports analogous equilibrium solutions for a star which is in uniform rotation.

scholarly journals Theory of quasi-stationary kinetic dynamos in magnetized accretion discs

2010 ◽  
Vol 6 (S274) ◽  
pp. 228-231 ◽  
Author(s):  
Claudio Cremaschini ◽  
John C. Miller ◽  
Massimo Tessarotto
Keyword(s):  
Magnetic Fields ◽  
Decisive Role ◽  
Accretion Disc ◽  
Compact Objects ◽  
Accretion Discs ◽  
Larmor Radius ◽  
Equilibrium Solutions ◽  
Temperature Anisotropy ◽  
Starting Point ◽  
Dynamo Effect

AbstractMagnetic fields are a distinctive feature of accretion disc plasmas around compact objects (i.e., black holes and neutron stars) and they play a decisive role in their dynamical evolution. A fundamental theoretical question related with this concerns investigation of the so-called gravitational MHD dynamo effect, responsible for the self-generation of magnetic fields in these systems. Experimental observations and theoretical models, based on fluid MHD descriptions of various types support the conjecture that accretion discs should be characterized by coherent and slowly time-varying magnetic fields with both poloidal and toroidal components. However, the precise origin of these magnetic structures and their interaction with the disc plasmas is currently unclear. The aim of this paper is to address this problem in the context of kinetic theory. The starting point is the investigation of a general class of Vlasov-Maxwell kinetic equilibria for axi-symmetric collisionless magnetized plasmas characterized by temperature anisotropy and mainly toroidal flow velocity. Retaining finite Larmor-radius effects in the calculation of the fluid fields, we show how these configurations are capable of sustaining both toroidal and poloidal current densities. As a result, we suggest the possible existence of a kinetic dynamo effect, which can generate a stationary toroidal magnetic field in the disc even without any net radial accretion flow. The results presented may have important implications for equilibrium solutions and stability analysis of accretion disc dynamics.

scholarly journals Magnetic Fields in Low-Mass Stars: An Overview of Observational Biases

2013 ◽  
Vol 9 (S302) ◽  
pp. 156-163 ◽  
Author(s):  
Ansgar Reiners
Keyword(s):  
Magnetic Fields ◽  
Zeeman Effect ◽  
Field Measurements ◽  
Rotating Stars ◽  
Magnetic Field Generation ◽  
Low Mass Stars ◽  
Important Indicator ◽  
Stellar Radius ◽  
Low Mass ◽  
Rapidly Rotating Stars

AbstractStellar magnetic dynamos are driven by rotation, rapidly rotating stars produce stronger magnetic fields than slowly rotating stars do. The Zeeman effect is the most important indicator of magnetic fields, but Zeeman broadening must be disentangled from other broadening mechanisms, mainly rotation. The relations between rotation and magnetic field generation, between Doppler and Zeeman line broadening, and between rotation, stellar radius, and angular momentum evolution introduce several observational biases that affect our picture of stellar magnetism. In this overview, a few of these relations are explicitly shown, and the currently known distribution of field measurements is presented.

scholarly journals Stellar dynamos with solar and antisolar differential rotations: Implications to magnetic cycles of slowly rotating stars

2019 ◽  
Vol 491 (3) ◽  
pp. 3155-3164 ◽  
Author(s):  
Bidya Binay Karak ◽  
Aparna Tomar ◽  
Vindya Vashishth
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Rotation Period ◽  
Toroidal Field ◽  
Dynamo Model ◽  
Cycle Period ◽  
Rotating Stars ◽  
Magnetic Cycles

ABSTRACT Simulations of magnetohydrodynamics convection in slowly rotating stars predict antisolar differential rotation (DR) in which the equator rotates slower than poles. This antisolar DR in the usual αΩ dynamo model does not produce polarity reversal. Thus, the features of large-scale magnetic fields in slowly rotating stars are expected to be different than stars having solar-like DR. In this study, we perform mean-field kinematic dynamo modelling of different stars at different rotation periods. We consider antisolar DR for the stars having rotation period larger than 30 d and solar-like DR otherwise. We show that with particular α profiles, the dynamo model produces magnetic cycles with polarity reversals even with the antisolar DR provided, the DR is quenched when the toroidal field grows considerably high and there is a sufficiently strong α for the generation of toroidal field. Due to the antisolar DR, the model produces an abrupt increase of magnetic field exactly when the DR profile is changed from solar-like to antisolar. This enhancement of magnetic field is in good agreement with the stellar observational data as well as some global convection simulations. In the solar-like DR branch, with the decreasing rotation period, we find the magnetic field strength increases while the cycle period shortens. Both of these trends are in general agreement with observations. Our study provides additional support for the possible existence of antisolar DR in slowly rotating stars and the presence of unusually enhanced magnetic fields and possibly cycles that are prone to production of superflare.

On the surface magnetic fields of rapidly rotating stars with winds

1988 ◽  
Vol 335 ◽  
pp. 931 ◽  
Author(s):  
Murugesapillai Maheswaran ◽  
Joseph P. Cassinelli
Keyword(s):  
Magnetic Fields ◽  
Rotating Stars ◽  
Rapidly Rotating Stars

scholarly journals Rotating Stars with Very Large Magnetic Fields

1971 ◽  
Vol 155 (2) ◽  
pp. 231-247 ◽  
Author(s):  
J. J. Monaghan ◽  
K. W. Robson
Keyword(s):  
Magnetic Fields ◽  
Rotating Stars
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