Magnetic Fields of Celestial Bodies

348 Pages·1994·15.519 MB·English

by  Ye Shi-Hui (auth.)

MAGNETIC FIELDS OF CELESTIAL BODIES
ASTROPHYSICS AND
SPACE SCIENCE LIBRARY
VOLUME 198
Executive Committee
W. B. BURTON, Sterrewacht, Leiden, The Netherlands
C. DE JAGER, Foundation Space Research, Utrecht, The Netherlands
E. P. 1. VA N DEN HEUVEL, Astronomical Institute, University ofA msterdam,
The Netherlands
H. VA N DER LAAN, Astronomical Institute, University of Utrecht,
The Netherlands
Editorial Board
I. APPENZELLER, Landessternwarte Heidelberg-Konigstuhl, Germany
J. N. BAHCALL, The Institute for Advanced Study, Princeton, U.S.A.
F. BERTOLA, Universita di Padova, Italy
W. B. BURTON, Sterrewacht, Leiden, The Netherlands
1. P. CASSINELLI, University of Wisconsin, Madison, U.S.A.
C.1. CESARSKY, Centre d'Etudes de Saclay, Gif-sur-Yvette Cedex, France
C. DE JAGER, Foundation Space Research, Utrecht, The Netherlands
R. McCRAY, University of Colorado, JILA, Boulder, U.S.A.
P. G. MURDIN, Royal Greenwich-Observatory, Cambridge, U.K.
F. PACINI, Istituto Astronomia Arcetri, Firenze, Italy
V. RADHAKRISHNAN, Raman Research Institute, Bangalore, India
F. H. SHU, University of California, Berkeley, U.S.A.
B. V. SOMOV, Astronomical Institute, Moscow State University, Russia
S. TREMAINE, CITA, University of Toronto, Canada
Y. TANAKA, Institute of Space & Astronautical Science, Kanagawa, Japan
E. P. 1. VA N DEN HEUVEL, Astronomical Institute, University ofA msterdam,
The Netherlands
H. VA N DEli'LAAN, Astronomical Institute, University of Utrecht,
The Netherlands
N. O. WEISS, University of Cambridge, U.K.
MAGNETIC FIELDS OF
CELESTIAL BODIES
by
YESHI-HUI
Purple Mountain Observatory and
Yunnan Astronomical Observatory,
Academia Sinica
SPRINGER SCIENCE+BUSINESS MEDIA, B.V.
A C.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-94-010-4407-3 ISBN 978-94-011-0944-4 (eBook)
DOI 10.1007/978-94-011-0944-4
Printed on acid-free paper
AII Rights Reserved
© 1994 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1994
Softcover reprint of the hardcover 1s t edition 1994
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permis sion from the copyright owner.
Dedicated to the memory of my late Soviet advisor,
Academician Andrei Borisovich Severny
(1913 - 1987)
Contents
Preface xiii
Acknowledgements xv
1 Introduction 1
1.1 A Brief Historical Account . . . . . . . . . 1
1.2 Significance of the Study of Cosmic Magnetic Fields .. 2
1.3 Electromagnetic Properties of Celestial Bodies . . . . . 5
1.3.1 Electrical Conductivity .............. .. . 5
1.3.2 Magnetic Coupling . . . . . . . . . . . . . . . . . . . 6
1.4 Present Status of the Study of Cosmic Magnetic Fields . . 7
2 Principles of Measurement of Magnetic Fields of Celestial
Bodies 9
2.1 Zeeman Effect. . . . . . . . . . . . . . . . . . . . 10
2.1.1 Basic Principles. . . . . . . . . . . . . . . 10
2.1.2 Patterns of Zeeman Splitting . . . . . . . 14
2.1.3 Relative Intensities of Zeeman Components ... . 14
2.1.4 Paschen-Back Effect . . . . . . . . . . . . . . . . . . 15
2.2 Inverse Zeeman Effect . . . . . . . . . . . . . . . . . . . . . 16
2.2.1 Direct and Inverse Zeeman Effects ......... . 16
2.2.2 Representation of Polarized Radiation . . . . . . . . 17
2.2.3 Unno's Theory of Spectral Line Formation in a
Magnetic Field ........ .. ........... 21
2.2.4 Stepanov's Theory of Spectral Line Formation in
the Magnetic Field . . . . . . . . . . . . . . . . . . . 24
2.3 Hanle Effect . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Faraday Rotation . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5 Radio Observations . . . . . . . . . . . . . . . . . . . . . . . 30
2.5.1 Non-Burst Solar Radio Emission ........ . 30
2.5.2 Solar Radio Bursts . . . . . . . . . . . . . . . . . . . 31
VB
viii CONTENTS
2.5.3 Occultation of External Radio Sources . . . . . . . . 32
2.6 Synchrotron Radiation . . . . . . . . . . . . . . . . . . . . . 32
2.7 Morphological Studies . . . . . . . . . . . . . . . . . . . . . 34
2.8 Theoretical Calculations and Other Methods . . . . . . . . 35
2.8.1 Calculation of the coronal magnetic field ...... 36
2.8.2 Equipartition of Magnetic and Kinetic Energies . . 37
3 Techniques for the Measurement of Magnetic Fields of
Celestial Bodies 41
3.1 Apparatus for Measuring Sunspot Magnetic Fields .... 41
3.1.1 Basic Principles . . . . . . . . . 41
3.1.2 Sources of Error . . . . . . . . . . . . . . . . 44
3.1.3 Theoretical Interpretation . . . . . . . . . . 45
3.1.4 Seares' Formula. . . . . . . . . . . . . . . . 47
3.2 Photoelectric Magnetographs . . . . . . . . . . . . 48
3.2.1 Fundamental Idea ................... 50
3.2.2 Construction ....................... 51
3.2.3 Interpretation of Magnetographic Recordings ... 53
3.2.4 New Instruments . . . . . . . . . . . . . . . . . . . . 56
3.3 Videomagnetographs ...................... 59
3.4 Vector Magnetographs . . . . . . . . . . . . . . . . . . . . . 60
3.4.1 Significance of Observation of the Transverse Com-
ponent .......................... 61
3.4.2 Fundamental Difficulty ......... . ...... 62
3.4.3 Basic Principles . . . . . . . . . . . . . . . . . . . . . 65
3.4.4 Comparison of Vector Magnetographs of Two Types 72
3.4.5 Methods of Calibration and Problem of 1800 Am-
biguity .......................... 74
3.5 Stokesmeters........................... 78
3.5.1 Basic Principles ..................... 78
3.5.2 Derivation of Information on the Magnetic Vector
from Stokes Profiles .................. 78
3.5.3 Stokes Polarimetry . . . . . . . . . . . . . . . . . . . 82
3.6 Influence of Stray Light and Instrumental Polarization . . 87
3.7 Selection of Magneto-Sensitive Spectral Lines . . . . . . . 90
4 The Magnetic Fields of Sunspots 95
4.1 Basic Characteristics ...................... 96
4.2 Orientation............................ 100
4.2.1 Angle Between Magnetic Lines of Force and Line
of Sight . . . . . . . . . . . . . . . . . . . . . . . . . . 100
CONTENTS ix
4.2.2 Azimuth . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.3 Fine Structures . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.4 3-D Models ............................ 111
4.4.1 Fan-Shaped Model ................... 111
4.4.2 Configuration of Magnetic Field Lines on the Spot
Surface Plane . . . . . . . . . . . . . . . . . . . . . . 113
4.4.3 Possible Twisting of Magnetic Field Lines ...... 114
4.4.4 Inclination of Magnetic Field Lines ......... 115
4.5 Sunspot Magnetic Fields and the Evershed Effect . . . . . 119
4.6 Magnetic Fields of Sunspot Groups and Complexes of Ac-
tivity ............................... 122
4.6.1 Magnetic Types of Spot Groups ............ 122
4.6.2 Magnetic Field Configurations of Complex Spots
and Spot Groups .................... 123
4.6.3 Magnetic Fields of Complexes of Activity . . . . . . 124
4.7 Influence of Magnetic Fields on Sunspot Spectra ...... 124
5 Background and Local Magnetic Fields on the Solar Sur-
face 129
5.1 Solar Background Magnetic Field ............... 129
5.1.1 "Hidden" Magnetic Fields ............... 130
5.1.2 Infrared Diagnostics .................. 131
5.1.3 Correlation of the Background Field with Other
Magnetic Structures . . . . . . . . . . . . . . . . . . 132
5.2 Small-Scale Magnetic Fields .................. 133
5.3 Magnetic Fields of Active Regions .............. 138
5.4 Large-Scale Magnetic Fields .................. 144
5.5 Solar Flares and Magnetic Fields . . . . . . . . . . . . . . . 150
5.5.1 Flare Energy Source and Storage. . . . . . . . . . . 150
5.5.2 Sudden Release of Flare Energy ........... 151
5.5.3 Changes of Local Magnetic Fields Before and After
Flares ........................... 153
5.5.4 Flares and Cancelling Magnetic Fields ....... 156
5.6 Magnetic Fields of Solar Prominences . . . . . . . . . . . . 158
6 Magnetic Fields of the Solar Atmosphere 163
6.1 Photospheric Magnetic Fields. . . . . . . . . . . .. 163
6.1.1 Granular Magnetic Fields ............... 163
6.1.2 Two-Component Model ................. 165
6.1.3 Physics of Photospheric Flux Tubes ......... 166
6.2 Chromospheric Magnetic Fields. . . . . . . . . . . . . . . . 168
x CONTENTS
6.3 Coronal Magnetic Fields . . . . . . . . . . . . . . . . . . . . 174
6.3.1 Inferences and Measurements ............ 174
6.3.2 Theoretical Calculations . . . . . . . . . . . . . . . . 176
6.3.3 Transient Changes . . . . . . . . . . . . . . . . . . . 178
6.4 Magnetic Field Gradient of the Solar Atmosphere . . . . . 178
6.4.1 Methods of Measurement ............... 179
6.4.2 Some Problems Associated With the Magnetic Field
Gradient . . . . . . . . . . . . . . . . . . . . . . . . . 183
6.4.3 Theoretical Limit of the Sunspot Magnetic Field
Gradient . . . . . . . . . . . . . . . . . . . . . . . . . 183
7 The General Magnetic Field of the Sun 185
7.1 Strength ofthe General Magnetic Field ....... 186
7.2 Fine Structures of the General Magnetic Field . . . . . 188
7.3 Polarity Reversals ofthe General Magnetic Field ..... 191
7.4 Rapid Changes of the General Magnetic Field .. . . . . . 194
7.5 The Global Magnetic Field of the Sun . . . . . . . . . . . . 197
7.5.1 Net Magnetic Flux of the Solar Disk ......... 197
7.5.2 Characteristics of the Global Field . . . . . . . . . . 198
7.5.3 Rapid Changes of the Global Field .......... 201
7.6 The Internal Magnetic Field of the Sun . ... ... 203
8 Magnetic Fields of the Solar System 207
8.1 Magnetic Field of Interplanetary Space . . . . . . . . . . . 207
8.1.1 Early Speculations . ...... ............ 207
8.1.2 The Coronal Expansion ................ 209
8.1.3 The Sectoral Structure . . . . . . ..... 210
8.2 Magnetospheres and the Heliosphere .......... .. 212
8.2.1 The Magnetosphere of the Earth ........... 212
8.2.2 Planetary Magnetospheres .............. 213
8.2.3 The Heliosphere. . . . . . . . . . . . . . . . . . . . . 215
8.3 The Lunar Magnetic Field ......... . .... .... . 216
8.3.1 Space and in situ Measurements ........... 216
8.3.2 Origin.......... . . . . .. ........... 217
8.4 Planetary Magnetic Fields ..... . ............. 219
8.4.1 Methods of Measurement ...... ... .... .. 220
8.4.2 A Brief Account of Observational Results . . . . . . 220
9 Stellar Magnetic Fields 223
9.1 Observations of Stellar Magnetic Fields .. . .224
9.1.1 The Pioneering Work of Babcock . . . . . . .. 224
CONTENTS Xl
9.1.2 Magnetographic Observations ............ 225
9.1.3 Diagnostic Methods ................... 226
9.2 Characteristics of Magnetic Stars ............... 228
9.3 Chemical Composition of Magnetic Stars .......... 232
9.3.1 Anomalies in Chemical Composition ......... 232
9.3.2 Inhomogeneous Distribution of Chemical Elements
on the Surface of Magnetic Stars . . . . . . . . . . . 234
9.4 Models of Magnetic Stars ................... 235
9.5 The Magnetic Field of Pulsars ................. 240
9.5.1 Discovery and Identification of Pulsars ... 240
9.5.2 Rotation and the Magnetic Field . . . . . .. 241
9.5.3 Superstrong Magnetic Fields . . . . . . . . . 242
9.5.4 Magnetic Dipole Model of Pulsars ... . . . 244
9.6 The Magnetic Field of White Dwarfs. . . . . . . . .245
10 Magnetic Fields of Galaxies and Intergalactic Space 251
10.1 The Interstellar Magnetic Field ................ 251
10.1.1 Evidence of Existence and Indirect Measurements 252
10.1.2 Direct Measurements. . . . . . . . . . . . . .254
10.1.3 Structure of the Galactic Magnetic Field .. 257
10.2 Magnetic Fields of Extragalactic Nebulae . . . . . 262
10.2.1 The Magellanic Clouds. . . . . . . . . . . . .263
10.2.2 Spiral Galaxies . . . . . . . . . . . . . . . . . 263
10.2.3 Clusters of Galaxies . ... . ....... . 265
11 Some Theoretical Problems of Cosmic Magnetic Fields 269
11.1 Theory of Spectral Line Formation in the Magnetic Field. 269
11.1.1 A Brief Historical Retrospect .......... .. . 270
11.1.2 Matrix Representation of the Transfer Equations . 271
11.1.3 Various Solutions of Equations of Transfer of Po-
larized Radiation . . . . . . . . . . . . . . . . . 273
11.2 Theory of the Sunspot Magnetic Field ............ 279
11.2.1 Basic Equations . . . . . . . . . . . . . . . . . . . . . 280
11.2.2 The Origin and Decay of the Sunspot Magnetic
Field ........................... 281
11.2.3 The Cooling of Sunspots . . . . . . . . . . . . . 282
11.2.4 The Stability of Sunspots . .............. 284
11.3 Theory of the Solar Activity Cycle .............. 286
11.3.1 Magnetic Buoyancy and Birth of Sunspots ..... 287
11.3.2 Drift of Sunspot Areas . . . . . . . . . . . . . . . . . 287
11.3.3 Interpretation of the Solar Magnetic Cycle . . . . . 291