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Stellar Dynamos

Published online by Cambridge University Press:  12 April 2016

F. Krause
F. Krause*
Affiliation:
Astrophysikalisches Institut Potsdam, D-O-1591 Potsdam, Rosa-Luxemburg-Str. 17a

Abstract

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Energy is transported from the central regions of a star to its surface. Generally this transport is in certain layers carried on by convective motions. Because of the structure, which these motions have due to the influence of the overall rotation, the star becomes electromagnetically unstable, i.e. a large magnetic field grows from small seed fields as a result of the dynamo process. The internal structure, especially the symmetries of a star, will be, at least to some extend, reflected by the spatial structure and the time behaviour of the excited magnetic field. In this sense observations of the magnetic field on a surface of a star and the related activity phenomena can provide insight in the internal structure of the star, since characteristic parameters like thickness of the convection zone, mixing length, turnover time, profile of the differential rotation, etc. strongly influence the dynamo process.

The actual magnetic field of a star is a product of a nonlinear process. Models elaborated on the kinematical (i.e. linear) level provide insight in the excitation conditions and the linear field modes. The marginal mode, i.e. the mode which is easiest to excite, reflects properties of the nonlinear solution in case the system operates not far from the margin to the dynamo unstable region. Here the solutions show symmetries with respect to the axis of rotation and the equatorial plane, properties which are, for example, to a large extend fulfilled for the solar average magnetic field. For systems operating far from this margin irregular or even chaotic behaviour has to be expected. From observations there is a strong indication that these theoretical possibilities find their realizations within the sample of late-type stars.

Type
VII. Activity, a break of spherical symmetry
Information
International Astronomical Union Colloquium , Volume 137: Inside the Stars , 1993 , pp. 578 - 590
Copyright
Copyright © Astronomical Society of the Pacific 1993

References

Baliunas, S. 1985, Ann. Rev. Astro. Astrophys., 23, 379 CrossRefGoogle Scholar
Belvedere, G., Proctor, M.R.E., Lanzafames, G. 1991, Nature, 350 Google Scholar
Brandenburg, A., Tuominen, I. 1991, The Sun and Cool Stars: activity, magnetism, dynamos, eds. Tuominen, I. Moss, D., Rüdiger, G., Springer-Verlag, 223 CrossRefGoogle Scholar
Brandenburg, A., Krause, F., Meinel, R., Moss, D., Tuominen, I., 1989a, Astron. Astrophys., 213, 411 Google Scholar
Brandenburg, A., Tuominen, I., Moss, D. 1989b, Geophys. Astrophys. Fluid Dynamics, 49, 129 CrossRefGoogle Scholar
Brandenburg, A., Krause, F., Tuominen, I. 1989c, in Turbulence and Nonlinear Dynamics in MHD Flows, eds. Meneguzzi, M. et al., Elsevier Science Publ., 35 Google Scholar
Brandenburg, A., Moss, D., Rüdiger, G., Tuominen, I. 1990a, Solar Physics, 128, 243 CrossRefGoogle Scholar
Brandenburg, A., Nordlund, A., Pulkkinen, P., Stein, R.T., Tuominen, I. 1990b, Astron. Astrophys., 232, 277 Google Scholar
Chan, K.L., Sofia, S. 1986, Astrophys. J., 307, 222 CrossRefGoogle Scholar
Chan, K.L., Sofia, S., Wolff, C.L. 1982,Astrophys. J, 263, 935 Google Scholar
Gilman, P.A. 1972, Solar Physics, 27, 3 CrossRefGoogle Scholar
Gilman, P.A. 1983, Astrophys. J. Suppl. Ser., 46, 211 Google Scholar
Glatzmaier, G.A. 1984, J. Comput. Phys., 55, 461 Google Scholar
Glatzmaier, G.A. 1985a, Astrophys. J., 291, 300 CrossRefGoogle Scholar
Glatzmaier, G.A. 1985b, Geophys. Astrophys. Fluid Dynamics, 31, 137 CrossRefGoogle Scholar
Harvey, J. 1988, Proc. Symp. Seismology of the Sun and Sun-like Stars, ESA SP-286, 55 Google Scholar
Jennings, R.L. 1991, Geophys. Astrophys. Fluid Dynamics, 57, 147 Google Scholar
Jennings, R.L., Weiss, N.O. 1991, Mon. Not. R. astr. Soc., 252, 249 Google Scholar
Jetsu, L., Huovelin, J., Tuominen, I., Vilhu, O., Bopp, B.W., Piirola, V. 1989, Astron. Astrophys., 236, 423 Google Scholar
Krause, F. 1971, Astron. Nachr., 293, 187 CrossRefGoogle Scholar
Krause, F. 1983, In Stellar and Planetary Magnetism, ed. Soward, A., Gordon and Breach Sc. Publ.Google Scholar
Krause, F. 1991, In The Sun and Cool Stars: activity, magnetism, dynamos, eds. Tuominen, I., Moss, D., Rudiger, G., Springer-Verlag, 1 Google Scholar
Krause, F., Rädier, K.-H. 1980, Mean-Field Magnetohydrodynamics and Dynamo Theory, Akademie Verlag Berlin, Pergamon Press Oxford Google Scholar
Krause, F., Meinel, R. 1988, Geophys. Astrophys. Fluid Dynamics, 43, 95 CrossRefGoogle Scholar
Larmor, J. 1919, Rep. Brit. Assoc. Adv. Sc., 1919, 159 Google Scholar
Libbrecht, K.J. 1988, Proc. Symp. Seismology of the Sun and Sun-like Stars, ESA SP-286, 131 Google Scholar
Moffatt, H.K. 1978, Magnetic Field Generation in Electrically Conducting Fluids, Cambridge University Press Google Scholar
Moss, D. 1990, Mon. Not. R. astr. Soc., 243, 537 Google Scholar
Moss, D. 1991, In The Sun and Cool Stars: Activity, Magnetism, Dynamos, eds. Tuominen, I., Moss, D., Rudiger, G., Springer-Verlag, 112 Google Scholar
Moss, D., Tuominen, I., Brandenburg, A. 1990, Astron. Astrophys., 240, 142 Google Scholar
Moss, D., Tuominen, I., Brandenburg, A. 1991, Astron. Astrophys., 245, 129 Google Scholar
Nordlund, A., Stein, R.F. 1989, In Solar and Stellar Granulation, eds. Rutten, R. and Severino, G., Kluwer Acad. Publ.Google Scholar
Oetken, L. 1977, Astron. Nachr., 298, 197 CrossRefGoogle Scholar
Oetken, L. 1979, Astron. Nachr., 300, 1 CrossRefGoogle Scholar
Piskunov, N.E., Tuominen, I., Vilhu, O. 1990, Astron. Astrophys., 230, 363 Google Scholar
Rädler, K.-H. 1980, Astron. Nachr., 301, 101 Google Scholar
Rädler, K.-H. 1983, In Stellar and Planetary Magnetism, ed. Soward, A., Gordon and Beach Sc. Publ., 37 Google Scholar
Rädler, K.-H. 1986, Astron. Nachr., 307, 89 Google Scholar
Rädler, K.-H., Wiedemann, E., Brandenburg, A., Meinel, R., Tuominen, I. 1990, Astron. Astrophys., 239, 413 Google Scholar
Roberts, P.H. 1972, Phil. Trans. Roy. Soc., A 272, 663 Google Scholar
Roberts, P.H., Stix, M. 1972, Astron. Astrophys., 18, 453 Google Scholar
Rüdiger, G. 1980, Astron. Nachr., 301, 181 Google Scholar
Rüdiger, G. 1989, Differential Rotation and Stellar Convection, Akademie Verlag Berlin, Gordon and Breach Google Scholar
Schrijver, C.J. 1991, In Reviews in Modern Astronomy, 4, ed. Klare, G., Springer-Verlag, 18 Google Scholar
Steenbeek, M., Krause, F. 1969, Astron. Nachr., 291, 49 Google Scholar
Stix, M. 1971, Astron. Astrophys., 13, 203 Google Scholar
Yoshimura, H. 1975a, Astrophys. J., 201, 740 Google Scholar
Yoshimura, H. 1975b, Astrophys. J. Suppl. Ser., 294, 467 Google Scholar
Zeldovich, Ya. B., Ruzmaikin, A.A., Sokoloff, D.D. 1983, Magnetic Fields in Astrophysics, Gordon and Beach Sc. Publ.Google Scholar