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Evolution of Stars and Stellar Populations Maurizio Salaris Astrophysics Research Institute, Liverpool John Moores University, UK Santi Cassisi INAF-Astronomical Observatory of Collurania, Teramo, Italy Evolution of Stars and Stellar Populations Evolution of Stars and Stellar Populations Maurizio Salaris Astrophysics Research Institute, Liverpool John Moores University, UK Santi Cassisi INAF-Astronomical Observatory of Collurania, Teramo, Italy Copyright © 2005 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone (+44) 1243 779777 Email (for orders and customer service enquiries): [email protected] Visit our Home Page on www.wiley.com All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP, UK, without the permission in writing of the Publisher. Requests to the Publisher should be addressed to the Permissions Department, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England, or emailed to [email protected], or faxed to (+44) 1243 770620. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The Publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the Publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Other Wiley Editorial Offices John Wiley & Sons Inc., 111 River Street, Hoboken, NJ 07030, USA Jossey-Bass, 989 Market Street, San Francisco, CA 94103-1741, USA Wiley-VCH Verlag GmbH, Boschstr. 12, D-69469 Weinheim, Germany John Wiley & Sons Australia Ltd, 33 Park Road, Milton, Queensland 4064, Australia John Wiley & Sons (Asia) Pte Ltd, 2 Clementi Loop #02-01, Jin Xing Distripark, Singapore 129809 John Wiley & Sons Canada Ltd, 22 Worcester Road, Etobicoke, Ontario, Canada M9W 1L1 Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress Cataloging in Publication Data Salaris, Maurizio. Evolution of stars and stellar populations / Maurizio Salaris, Santi Cassisi. p. cm. Includes bibliographical references and index. ISBN-13 978-0-470-09219-X (cloth : alk. paper) ISBN-10 0-470-09219-X (cloth : alk. paper) ISBN-13 978-0-470-09220-3 (pbk. : alk. paper) ISBN-10 0-470-09220-3 (pbk. : alk. paper) 1. Stars—Evolution. 2. Stars—Populations. 3. Galaxies—Evolution. I. Cassisi, Santi. II. Title. QB806.S25 2005 523.88—dc22 2005021402 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN-13 978-0-470-09219-X (HB) 978-0-470-09220-3 (PB) ISBN-10 0-470-09219-X (HB) 0-470-09220-3 (PB) Typeset in 10.5/12.5pt Times by Integra Software Services Pvt. Ltd, Pondicherry, India Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire This book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least two trees are planted for each one used for paper production. To Suzanne and my parents To all the people who really loved me Contents Preface xi 1 Stars and the Universe 1 1.1 Setting the stage 1 1.2 Cosmic kinematics 5 1.2.1 Cosmological redshifts and distances 8 1.3 Cosmic dynamics 13 1.3.1 Histories of Rt 14 1.4 Particle- and nucleosynthesis 17 1.5 CMB fluctuations and structure formation 24 1.6 Cosmological parameters 25 1.7 The inflationary paradigm 26 1.8 The role of stellar evolution 28 2 Equation of State of the Stellar Matter 31 2.1 Physical conditions of the stellar matter 31 2.1.1 Fully ionized perfect gas 35 2.1.2 Electron degeneracy 38 2.1.3 Ionization 41 2.1.4 Additional effects 44 3 Equations of Stellar Structure 49 3.1 Basic assumptions 49 3.1.1 Continuity of mass 50 3.1.2 Hydrostatic equilibrium 50 3.1.3 Conservation of energy 52 3.1.4 Energy transport 52 3.1.5 The opacity of stellar matter 66 3.1.6 Energy generation coefficient 68 3.1.7 Evolution of chemical element abundances 83 3.1.8 Virial theorem 86 3.1.9 Virial theorem and electron degeneracy 89 3.2 Method of solution of the stellar structure equations 90 3.2.1 Sensitivity of the solution to the boundary conditions 97 3.2.2 More complicated cases 98 viii CONTENTS 3.3 Non-standard physical processes 99 3.3.1 Atomic diffusion and radiative levitation 100 3.3.2 Rotation and rotational mixings 102 4 Star Formation and Early Evolution 105 4.1 Overall picture of stellar evolution 105 4.2 Star formation 106 4.3 Evolution along the Hayashi track 110 4.3.1 Basic properties of homogeneous, fully convective stars 110 4.3.2 Evolution until hydrogen burning ignition 114 5 The Hydrogen Burning Phase 117 5.1 Overview 117 5.2 The nuclear reactions 118 5.2.1 The p–p chain 118 5.2.2 The CNO cycle 119 5.2.3 The secondary elements: the case of 2H and 3He 121 5.3 The central H-burning phase in low main sequence (LMS) stars 123 5.3.1 The Sun 125 5.4 The central H-burning phase in upper main sequence (UMS) stars 128 5.5 The dependence of MS tracks on chemical composition and convection efficiency 133 5.6 Very low-mass stars 136 5.7 The mass–luminosity relation 138 5.8 The Schönberg–Chandrasekhar limit 140 5.9 Post-MS evolution 141 5.9.1 Intermediate-mass and massive stars 141 5.9.2 Low-mass stars 142 5.9.3 The helium flash 148 5.10 Dependence of the main RGB features on physical and chemical parameters 149 5.10.1 The location of the RGB in the H–R diagram 150 5.10.2 The RGB bump luminosity 151 5.10.3 The luminosity of the tip of the RGB 152 5.11 Evolutionary properties of very metal-poor stars 155 6 The Helium Burning Phase 161 6.1 Introduction 161 6.2 The nuclear reactions 161 6.3 The zero age horizontal branch (ZAHB) 163 6.3.1 The dependence of the ZAHB on various physical parameters 165 6.4 The core He-burning phase in low-mass stars 167 6.4.1 Mixing processes 167 CONTENTS ix 6.5 The central He-burning phase in more massive stars 173 6.5.1 The dependence of the blue loop on various physical parameters 175 6.6 Pulsational properties of core He-burning stars 179 6.6.1 The RR Lyrae variables 181 6.6.2 The classical Cepheid variables 183 7 The Advanced Evolutionary Phases 187 7.1 Introduction 187 7.2 The asymptotic giant branch (AGB) 187 7.2.1 The thermally pulsing phase 189 7.2.2 On the production of s-elements 194 7.2.3 The termination of the AGB evolutionary phase 195 7.3 The Chandrasekhar limit and the evolution of stars with large CO cores 198 7.4 Carbon–oxygen white dwarfs 199 7.4.1 Crystallization 206 7.4.2 The envelope 210 7.4.3 Detailed WD cooling laws 212 7.4.4 WDs with other chemical stratifications 213 7.5 The advanced evolutionary stages of massive stars 214 7.5.1 The carbon-burning stage 217 7.5.2 The neon-burning stage 219 7.5.3 The oxygen-burning stage 220 7.5.4 The silicon-burning stage 221 7.5.5 The collapse of the core and the final explosion 222 7.6 Type Ia supernovae 224 7.6.1 The Type Ia supernova progenitors 225 7.6.2 The explosion mechanisms 229 7.6.3 The light curves of Type Ia supernovae and their use as distance indicators 230 7.7 Neutron stars 233 7.8 Black holes 236 8 From Theory to Observations 239 8.1 Spectroscopic notation of the stellar chemical composition 239 8.2 From stellar models to observed spectra and magnitudes 241 8.2.1 Theoretical versus empirical spectra 248 8.3 The effect of interstellar extinction 250 8.4 K-correction for high-redshift objects 253 8.5 Some general comments about colour–magnitude diagrams (CMDs) 254 9 Simple Stellar Populations 259 9.1 Theoretical isochrones 259 9.2 Old simple stellar populations (SSPs) 264 9.2.1 Properties of isochrones for old ages 264 9.2.2 Age estimates 268 x CONTENTS 9.2.3 Metallicity and reddening estimates 281 9.2.4 Determination of the initial helium abundance 284 9.2.5 Determination of the initial lithium abundance 287 9.2.6 Distance determination techniques 289 9.2.7 Luminosity functions and estimates of the IMF 301 9.3 Young simple stellar populations 304 9.3.1 Age estimates 304 9.3.2 Metallicity and reddening estimates 309 9.3.3 Distance determination techniques 310 10 Composite Stellar Populations 315 10.1 Definition and problems 315 10.2 Determination of the star formation history (SFH) 320 10.3 Distance indicators 327 10.3.1 The planetary nebula luminosity function (PNLF) 329 11 Unresolved Stellar Populations 331 11.1 Simple stellar populations 331 11.1.1 Integrated colours 334 11.1.2 Absorption-feature indices 341 11.2 Composite stellar populations 347 11.3 Distance to unresolved stellar populations 347 Appendix I: Constants 351 Appendix II: Selected Web Sites 353 References 357 Index 369 Preface The theory of stellar evolution is by now well established, after more than half a century of continuous development, and its main predictions confirmed by various empirical tests.
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