P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 THE ORIGIN AND EVOLUTION OF PLANETARY NEBULAE SUN KWOK University of Calgary, Canada iii P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 PUBLISHED BY THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE The Pitt Building, Trumpington Street, Cambridge, United Kingdom CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 2RU, UK http://www.cup.cam.ac.uk 40 West 20th Street, New York, NY 10011-4211, USA http://www.cup.org 10 Stamford Road, Oakleigh, Melbourne 3166, Australia Ruiz de Alarc´on 13, 28014 Madrid, Spain c Cambridge University Press 2000 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2000 Printed in the United States of America Typeface Times Roman 10.5/12.5 pt. and Gill Sans System LATEX2ε [TB] A catalog record for this book is available from the British Library. Library of Congress Cataloging in Publication Data Kwok, S. (Sun) The origin and evolution of planetary nebulae / Sun Kwok. p. cm. – (Cambridge astrophysics series : 33) ISBN 0-521-62313-8 (hc.) 1. Planetary nebulae. I. Title. II. Series. QB855.5.K96 1999 523.10135 – dc21 99-21392 CIP ISBN 0 521 62313 8 hardback iv P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 Contents Preface page xiii 1 History and overview 1 1.1 Planetary nebulae as a phase of stellar evolution 2 1.2 Discovery and identification 3 1.3 Confusion with other galactic objects 4 1.4 Plantary nebulae as a physics laboratory 7 2 Ionization structure of planetary nebulae 9 2.1 Photoionization 9 2.2 Recombination 13 2.3 Ionization structure of a static nebula 16 2.4 Ionization of complex atoms 17 2.5 Dielectric recombination 18 2.6 Charge-exchange reactions 19 3 Nebular line radiation 20 3.1 Permitted and forbidden transitions 20 3.2 Absorption and emission 24 3.3 Thermodynamic equilibrium versus steady state 27 3.4 Recombination lines 28 3.5 Collisionally excited lines 32 3.6 Determination of nebular density and temperature by diagnostic diagrams 36 3.7 Resonance fluorescence for OIII 37 3.8 Forbidden lines of less-abundant elements 37 3.9 Determination of the rest wavelengths of forbidden lines 38 3.10 Optical spectroscopic surveys of PN 39 4 Nebular continuum radiation 40 4.1 Free-bound continuum radiation 40 4.2 Two-photon radiation 41 4.3 Free-free continuum emission 44 vii P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 viii Contents 4.4 Radio observations of planetary nebulae 47 4.5 Determination of the nebular mass 50 5 The neutral gas component 53 5.1 Physics of diatomic molecules 53 5.2 Rotational transitions 54 5.3 Molecular line profile in an expanding envelope 57 5.4 CO in planetary nebulae 60 5.5 Molecular gas distribution in PN 60 5.6 OH in planetary nebulae 60 5.7 Molecular hydrogen emission 61 5.8 Emission from neutral atoms 64 5.9 Circumstellar chemistry 65 6 The dust component 67 6.1 Dust absorption and emission 67 6.2 Dust continuum emission from planetary nebulae 70 6.3 Dust features 70 6.4 Radiative coupling between the ionized, dust, and neutral gas components 72 6.5 Summary 74 7 Observations of the central star of planetary nebulae 75 7.1 Determination of the temperature of the central star 75 7.2 Spectral classification of the central stars 79 7.3 PG 1159 stars 82 7.4 Model atmospheres 82 7.5 Winds from the central star 83 7.6 Extreme UV and X-ray emission from CSPN 86 7.7 PN with binary central stars 86 7.8 Summary 87 8 Morphologies of planetary nebulae 89 8.1 Morphological classifications 89 8.2 Relationship between nebular morphology and central-star evolution 91 8.3 Optical imaging techniques 92 8.4 Halos around planetary nebulae 94 8.5 Microstructures 94 8.6 Origin of PN morphology 96 9 Problems and questions 101 10 Asymptotic giant branch stars – progenitors of planetary nebulae 103 10.1 Structure of AGB stars 104 10.2 Photospheric composition of AGB stars 105 P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 Contents ix 10.3 Pulsation on the AGB 106 10.4 Mass loss on the AGB 106 10.5 Mechanisms of mass loss on the AGB 110 10.6 AGB evolution with mass loss 112 10.7 Initial mass–final mass relationship 113 10.8 Summary 115 11 Evolution of the central stars 116 11.1 The modern era 117 11.2 Evolutionary models with mass loss and thermal pulses 118 11.3 On the existence of PN 120 11.4 Helium-burning central stars 121 11.5 Discrepancy between the dynamical and evolutionary ages 122 11.6 Summary 123 12 Formation of planetary nebulae 124 12.1 Effects of AGB mass loss on the formation of planetary nebulae 125 12.2 The interacting stellar winds model 125 12.3 Transition from the momentum-conserving case to the energy-conserving case 130 12.4 Observational confirmations of the ISW model 131 12.5 Summary 131 13 Dynamical evolution of planetary nebulae 134 13.1 Variability of the central-star wind 135 13.2 Nebular acceleration 137 13.3 Time-dependent ionization structure 137 13.4 Heating and cooling 139 13.5 Expansion velocity of PN 140 13.6 The three-wind model 140 13.7 Derivation of nebular properties from dynamical models 141 13.8 Evolution of the dust component 144 13.9 Shaping of planetary nebulae 145 13.10 Asymmetric ionization structure of PN 148 13.11 Summary 149 14 Protoplanetary nebulae – the transition objects 151 14.1 Early PPN candidates 152 14.2 The Search for PPN 153 14.3 Optical properties of PPN 157 14.4 Infrared properties of PPN 158 14.5 Circumstellar molecular emissions 163 14.6 The beginning of photoionization 164 14.7 Morphologies of PPN 165 14.8 Summary 165 P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 x Contents 15 Evolution to the white dwarf stage 167 15.1 Structure of white dwarfs 168 15.2 Cooling of white dwarfs 170 15.3 Envelope chemical composition 171 15.4 Subluminous O stars 171 15.5 Transition objects between PN central stars and WDs 171 15.6 Luminosity function of white dwarfs 172 15.7 Mass distribution 173 15.8 White dwarfs in external galaxies 173 15.9 White dwarfs as contributors to dark matter 175 15.10 Birth rate of white dwarfs 175 15.11 Summary 176 16 Distances to planetary nebulae 177 16.1 Statistical distances 177 16.2 Other methods of distance determination 181 16.3 Summary 184 17 Comparison between evolutionary models and observations 185 17.1 Are PN ionization bounded? 185 17.2 PN with reliable distances 186 17.3 Test of PN evolutionary models by distance-independent parameters 186 17.4 Mass distribution of CSPN 188 17.5 Asteroseismology of CSPN 188 17.6 Summary 189 18 PN in the galactic context 190 18.1 Formation rate of PN in the Galaxy 191 18.2 The death rate of main-sequence stars 191 18.3 Effects of metallicity on the formation of planetary nebulae 193 18.4 Nearby PN 194 18.5 PN in the galactic bulge 194 18.6 PN in the galactic halo 195 18.7 Galactic distribution of PN with different core masses 195 18.8 Mass returned to the Galaxy 196 18.9 Contribution by post-AGB stars to the ultraviolet excess in galaxies 196 18.10 Summary 198 19 Chemical abundances 199 19.1 Chemical abundances in planetary nebulae 199 19.2 Isotopic abundances 200 19.3 PN abundances in different galactic systems 201 19.4 The relation between chemical abundances and core masses 204 19.5 Chemical abundances in post-AGB stars 206 19.6 Summary 207 P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-FM CB211/Kwok October 30, 1999 1:26 Char Count= 0 Contents xi 20 Planetary nebulae in other galaxies 208 20.1 Planetary nebulae in the Magellanic Clouds 208 20.2 Galactic evolution 209 20.3 Planetary nebulae as distance indicators 209 20.4 Planetary nebulae as tracers of dark matter 216 21 Concluding remarks 221 References 223 Appendix 1 List of symbols and abbreviations 237 Appendix 2 Subject index 241 P1: MRM/SPH P2: MRM/UKS QC: MRM/UKS T1: MRM CB211-01 October 6, 1999 21:34 Char Count= 0 1 History and overview The first planetary nebula was observed by Charles Messier in 1764 and was given the number 27 in his catalog of nebulous objects. The final version of the Messier catalog of 1784 included four planetary nebulae (PN) together with other nonstarlike objects such as galaxies and star clusters. The name planetary nebulae was given by William Herschel, who found that their appearances resembled the greenish disk of a planet.