An Introduction to Astrophysics

598 Pages·2010·25.367 MB·English

by  Baidyanath Basu, Tanuka Chattopadhyay, Sudhindra Nath Biswas

Eastern
Economy
Edition
Second Edition
AN INTRODUCTION TO
ASTROPHYSICS
Tanuka Chattopadhyay
Sudhindra Nath Biswas
An Introduction to
ASTROPHYSICS
SECOND EDITION
Baidyanath Basu
Formerly Professor and Head
Department of Applied Mathematics
University of Calcutta
Tanuka Chattopadhyay
Department of Applied Mathematics
University of Calcutta
Sudhindra Nath Biswas
PHI Learning Private Limited
New Delhi-110 001
2010
AN INTRODUCTION TO ASTROPHYSICS, Second Edition
Baidyanath Basu, Tanuka Chattopadhyay and Sudhindra Nath Biswas
© 2010 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may
be reproduced in any form, by mimeograph or any other means, without permission in writing from
the publishers.
ISBN-978-81-203-4071-8
The export rights of this book are vested solely with the publisher.
Seventh Printing (Second Edition) June, 2010
Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus,
New Delhi-110001 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC,
Kundli-131028, Sonepat, Haryana.
To
the loving memory of my parents
Bisweswar Basu
Charushila Basu
— Baidyanath Basu
Contents
Foreword xiii
Preface xv
Preface to the First Edition xvii
1. ASTRONOMICAL INSTRUMENTS 1-26
1.1 Light and Its Properties 1
1.2 The Earth’s Atmosphere and the Electromagnetic Radiation 6
1.3 Optical Telescopes 7
1.4 Radio Telescopes 12
1.5 The Hubble Space Telescope (HST) 75
1.6 Astronomical Spectrographs 16
1.7 Photographic Photometry 27
1.8 Photoelectric Photometry 22
1.9 Spectrophotometry 23
1.10 Detectors and Image Processing 24
Exercises 25
Suggested Reading 26
2. BASIC PHYSICS 27-55
2.1 Planck’s Theory of Blackbody Radiation 27
2.2 Photoelectric Effect 30
2.3 Pressure of Radiation 31
2.4 Continuous, Absorption and Emission Spectra—Kirchhoff’s Laws 33
2.5 Doppler Effect 34
2.6 Zeeman Effect 35
2.7 Bohr’s Concept of the H-atom 37
2.8 Molecular Spectra 42
2.9 Bremsstrahlung 43
2.10 Synchrotron Radiation 45
2.11 Scattering of Radiation 48
2.12 Compton Effect and Inverse Compton Effect 57
Exercises 54
Suggested Reading 55
V
vi Contents
3. MAGNITUDES, MOTIONS AND DISTANCES OF STARS 56-76
3.1 Stellar Magnitude Sequence 56
3.2 Absolute Magnitude and the Distance Modulus 57
3.3 The Bolometric Magnitude 59
3.4 Different Magnitude Standards: The UBV System and
Six-colour Photometry 59
3.5 Radiometric Magnitudes 60
3.6 The Colour-index of a Star 61
3.1 Luminosities of Stars 62
3.8 Stellar Parallax (Trigonometric) and the Units of Stellar Distances 63
3.9 Stellar Positions: The Celestial Coordinates 64
3.10 Stellar Motions 67
3.11 The Solar Motion and the Peculiar Velocities of Stars 69
3.12 The Velocity Dispersion 71
3.13 Statistical Parallax 71
3.14 Moving Cluster Parallax 73
Exercises 75
Suggested Reading 76
4. SPECTRAL CLASSIFICATION OF STARS 77-98
4.1 Introduction 77
4.2 Boltzmann’s Formula 78
4.3 Saha’s Equation of Thermal Ionization 79
4.4 Harvard System of Spectral Classification:
The Henry-Draper (HD) Catalogue 82
4.5 The Luminosity Effect on Stellar Spectra 85
4.6 Importance of Ionization Theory in Astrophysics 87
4.7 Spectroscopic Parallax 90
4.8 The Hertzsprung-Russell Diagram 91
Exercises 97
Suggested Reading 98
5. THE SUN 99-135
5.1 Sun—A Typical Star 99
5.2 The Photosphere: Limb-darkening 101
5.3 Solar Granulation 102
5.4 Faculae 105
5.5 The Chromosphere 106
5.6 Solar Corona 107
5.7 Prominences 110
5.8 The 11-year Solar Cycle and Sunspots 113
5.9 The Solar Magnetic Fields 117
5.10 Theory of Sunspots 120
5.11 Solar Flares 123
Contents vii
5.12 Radio Emission from the Sun 126
5.13 Solar Wind 129
5.14 The Solar Neutrino Puzzle 130
Exercises 134
Suggested Reading 135
6. ATMOSPHERE OF STARS 136-177
6.1 Introduction 136
6.2 Some Important Definitions 137
6.3 The Equation of Transfer 141
6.4 The Solution of the Equation of Transfer 144
6.5 Processes of Absorption in Stellar Atmospheres 150
6.6 Continuous Absorption by the Negative Hydrogen Ions (H-) in
Cooler Stars 156
6.7 Analysis of Spectral Line Broadening 157
6.8 The Curve of Growth 166
6.9 Stellar Temperatures 169
6.10 The Chemical Composition of Stars 170
Exercises 176
Suggested Reading 177
7. BINARY AND MULTIPLE STARS 178-193
7.1 Introduction 178
7.2 Visual Binary 179
7.3 Spectroscopic Binary 182
7.4 Eclipsing Binary 183
7.5 Multiple Stars 186
7.6 Origin of Binary Stars 187
7.7 Stellar Masses and Mass-luminosity Relation 188
7.8 Mass Transfer in Close Binary Systems 190
Exercises 192
Suggested Reading 193
8. VARIABLE STARS 194-212
8.1 Classification of Variable Stars 194
8.2 The Cepheid Group of Variables 195
8.3 Period-luminosity Relations of Cepheid Group of Variables 201
8.4 RV Tauri Variables 202
8.5 Long-period Variables (Mira-type Variables) 203
8.6 Red Irregular and Semi-regular Variables 205
8.7 Beta Canis Majoris Variables (β Cephei Stars) 205
8.8 U Geminorum Stars (SS Cygni or Dwarf Novae) 206
8.9 Flare Stars 206
8.10 A Survey of Variable Stars as a Whole 207
viii Contents
8.11 The Pulsation Theory of Variable Stars 208
Exercises 210
Suggested Reading 211
9. ERUPTING AND EXPLODING STARS 213-225
9.1 Introduction 213
9.2 Distribution of Novae in Our Galaxy 214
9.3 Determination of Distance and Luminosity of Novae 214
9.4 Light Variation of Novae 215
9.5 Spectra of Novae 217
9.6 Cause of Nova Outburst 219
9.7 Supernovae 220
9.8 SN 1987 A 223
Exercises 224
Suggested Reading 225
10. MORE STARS OF INTEREST 226-255
Sioenct A: Stars with Extended Atmospheres
10.1 The Wolf-Rayet Stars 226
10.2 P Cygni and a Cygni Stars 229
10.3 Be Stars: Shell Stars 230
10.4 Of Stars 232
Sioenct B: Some Cooler Stars of Interest
10.5 Peculiar A Stars and Metallic-line A Stars 233
10.6 T Tauri Stars 237
10.7 The Emission-line Red Dwarf (dMe) Stars 238
10.8 R Coronae Borealis (R Cor Bor) Stars 239
10.9 The Carbon Stars (R and N Stars) 240
10.10 The Heavy-metal Oxide Stars (S Stars) 241
10.11 Infrared Stars 241
10.12 Subdwarfs 243
10.13 Brown Dwarfs 244
Exercises 254
Suggested Reading 254
11. CLUSTERS AND ASSOCIATIONS OF STARS 256-276
11.1 Introduction 256
11.2 Galactic Clusters 257
11.3 Globular Clusters 262
11.4 Stellar Associations 266
11.5 Stellar Population Characteristics 268
11.6 Star Formation 271
Exercises 275
Suggested Reading 276
Contents ix
12. GALACTIC NEBULAE 277-309
12.1 Introduction 277
12.2 Classification and Galactic Distribution of Nebulae 279
12.3 Observational Techniques 281
12.4 Dark Nebulae 283
12.5 Reflection Nebulae 286
12.6 Diffuse Emission Nebulae: Theory of Emission Lines 287
12.7 Planetary Nebulae 295
12.8 The Crab Nebula: Supernova Remnants 303
Exercises 307
Suggested Reading 308
13. INTERSTELLAR MATTER 310-342
13.1 Large-scale Distribution of Interstellar Matter 310
13.2 Interstellar Lines 312
13.3 Interstellar Clouds 317
13.4 H I and H II Regions: Strömgren’s Spheres 319
13.5 Interstellar Shock Waves 324
13.6 Interstellar Cloud Collisions 332
13.7 Energy Balance in Interstellar Gas 333
13.8 The Intercloud Medium 336
13.9 Interstellar Grains 337
Exercises 340
Suggested Reading 342
14. STRUCTURE AND EVOLUTION OF STARS 343-374
14.1 Introduction 343
14.2 The Observational Basis 344
14.3 The Equation of State for Stellar Interior 346
14.4 Mechanical and Thermal Equilibrium in Stars 348
14.5 Energy Transport in Stellar Interior 351
14.6 Energy Generation in Stars 354
14.7 Stellar Evolution 361
14.8 White Dwarfs 367
Exercises 372
Suggested Reading 373
15. NEUTRON STARS AND BLACK HOLES 375-389
15.1 Discovery of Pulsars 375
15.2 Rotating Neutron Star Model of Pulsars 376
15.3 Period Distribution and Loss of Rotational Energy 377
15.4 Test of Rotating Neutron Star Model of Pulsars 379
15.5 Gold’s Model of Pulsars 380
X Contents
15.6 Distance and Distribution of Pulsars 382
15.7 Binary Pulsars 384
15.8 Black Holes 385
Exercises 388
Suggested Reading 389
16. OUR GALAXY 390-426
16.1 Introduction 390
16.2 Rotation of the Galaxy: Differential Rotation 393
16.3 Determination of the Rotation Parameters in the Solar Neighbourhood 398
16.4 Radio Observation of the Galaxy at 21-cm Wave Length 401
16.5 The Rotation Curve of the Galaxy: The General Rotation Law 403
16.6 Density Distribution of Gas and Spiral Structure of the Galaxy:
Radio and Optical Data 406
16.7 The General Structure of the Galaxy 409
16.8 The Mass of the Galaxy 414
16.9 Magnetic Field in the Galaxy 416
16.10 Cosmic Rays 420
16.11 Continuous Radio Emission in the Galaxy 422
Exercises 424
Suggested Reading 426
17. EXTERNAL GALAXIES 427-474
17.1 Introduction 42 7
17.2 Classification of Galaxies 428
17.3 Distribution of Galaxies 434
17.4 Luminosity Distribution of Galaxies 435
17.5 Spectra of Galaxies 437
17.6 The Local Group of Galaxies 439
17.7 Distances of Galaxies 440
17.8 Nuclei of Galaxies 444
17.9 Theories of Spiral Structures of Disk Galaxies 446
17.10 Dwarf Galaxies 455
17.11 Ultra Compact Dwarf Galazies (UCD) 462
17.12 Compact Groups of Galaxies 464
Exercises 470
Suggested Reading 471
18. CLUSTERS OF GALAXIES 475-505
18.1 Clustering Nature of Galaxies 475
18.2 Morphological Classification of Clusters 478
18.3 cD Galaxies 480
18.4 Interacting Galaxies and Galaxy Mergers 481