scholarly journals 18. Stellar magnetic fields

1958 ◽  
Vol 6 ◽  
pp. 161-165
Author(s):  
Horace W. Babcock
Keyword(s):  
Magnetic Fields ◽  
Large Amplitude ◽  
Zeeman Effect ◽  
Type A ◽  
Magnetic Fluctuations ◽  
Sharp Line ◽  
Stellar Magnetic Fields ◽  
Observational Program

A report is given of a ten-year observational program directed toward the discovery and investigation of the magnetic fields of stars through the Zeeman effect in their spectra. The emphasis has been on the sharp-line stars of type A, of which ten have been found to show irregular magnetic fluctuations without reversal of polarity, ten others to fluctuate irregularly with occasional reversals of polarity, and six to show essentially periodic variations; of the latter group, four are large-amplitude reversers with periods near one week.

scholarly journals Recent measurements of stellar magnetic fields

1996 ◽  
Vol 176 ◽  
pp. 237-244 ◽  
Author(s):  
S. H. Saar
Keyword(s):  
Magnetic Fields ◽  
Filling Factor ◽  
Zeeman Effect ◽  
Active Regions ◽  
Small Magnitude ◽  
Yield Information ◽  
Cool Stars ◽  
Surface Filling ◽  
The Mean ◽  
Stellar Magnetic Fields

High resolution, high S/N spectra have been successfully modeled to yield information on the magnetic properties of cool stars for some 15 years now. These analyses yield estimates of the intensity weighted surface filling factor of active regions, f, and the mean unsigned field strength in these regions), B. The measurements are difficult, though, hampered by the small magnitude of the Zeeman effect, small f values for most stars, and the unknown spatial and thermodynamic properties of the active regions. Recent data, mostly in the infrared (IR) where the Zeeman effect (∞ λ2) is larger, are yielding better measurements than ever before. I summarize the new observations here, and show how they are expanding and modifying our understanding of magnetic fields on cool stars.

scholarly journals Cyclic fluctuations in the differential rotation of active stars

2006 ◽  
Vol 2 (14) ◽  
pp. 280-281
Author(s):  
Pascal Petit
Keyword(s):  
Magnetic Fields ◽  
Differential Rotation ◽  
Time Scale ◽  
Large Amplitude ◽  
Modeling Tools ◽  
Temporal Fluctuations ◽  
Active Stars ◽  
Stellar Magnetic Fields ◽  
The Impact ◽  
Stellar Dynamo

AbstractDifferential rotation is described in stellar dynamo models as one of the fundamental phenomena governing the amplification of magnetic fields in active stars.Using indirect imaging methods, the measurement of photospheric differential rotation is now achieved on a growing number of very active stars, a fraction of which exhibit temporal fluctuations of potentially large amplitude in their latitudinal shear, on a time-scale of a few years. I first describe the modeling tools on which such analysis is based, then discuss the implications of this observational work on our understanding of stellar dynamos and of the impact stellar magnetic fields may have on the dynamics of convective envelopes.

scholarly journals The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

2005 ◽  
Vol 444 (3) ◽  
pp. 947-960 ◽  
Author(s):  
S. V. Berdyugina ◽  
P. A. Braun ◽  
D. M. Fluri ◽  
S. K. Solanki
Keyword(s):  
Magnetic Fields ◽  
Zeeman Effect ◽  
Stellar Magnetic Fields

scholarly journals The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

2003 ◽  
Vol 412 (2) ◽  
pp. 513-527 ◽  
Author(s):  
S. V. Berdyugina ◽  
S. K. Solanki ◽  
C. Frutiger
Keyword(s):  
Magnetic Fields ◽  
Zeeman Effect ◽  
Stellar Magnetic Fields

scholarly journals Infrared Measurements of Stellar Magnetic Fields

1994 ◽  
Vol 154 ◽  
pp. 437-447 ◽  
Author(s):  
Steven H. Saar
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Pressure Support ◽  
Field Research ◽  
Future Directions ◽  
Rotation Rates ◽  
Infrared Measurements ◽  
Cool Stars ◽  
Rs Cvn Variables ◽  
Stellar Magnetic Fields

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.

Observation of magnetic fields in laser-produced plasma using the Zeeman effect

1984 ◽  
Vol 27 (5) ◽  
pp. 1327 ◽  
Author(s):  
E. A. McLean ◽  
J. A. Stamper ◽  
C. K. Manka ◽  
H. R. Griem ◽  
D. W. Droemer ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Zeeman Effect ◽  
Laser Produced Plasma

scholarly journals Global MHD phenomena and their importance for stellar surfaces

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.

The macrodynamics of α-effect dynamos in rotating fluids

1975 ◽  
Vol 67 (3) ◽  
pp. 417-443 ◽  
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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