Old Stellar Populations: How to Study the Fossil Record of Galaxy Formation

The book discusses the theoretical path to decoding the information gathered from observations of old stellar systems. It focuses on old stellar systems because these are the fossil record of galaxy formation and provide invaluable information ont he evolution of cosmic structures and the universe as a whole. The aim is to present results obtained in the past few years for theoretical developments in low mass star research and in advances in our knowledge of the evolution of old stellar systems. A particularly representative case is the recent discovery of multiple stellar populations in galactic globular clusters that represents one of the hottest topics in stellar and galactic astrophysics and is discussed in detail.

Santi Cassisi has authored about 270 scientific papers, 150 of them in peer-reviewed journals, and the title Evolution of Stars and Stellar Populations.

Preface XIII

1 Introduction 1

1.1 Galaxy Formation 4

1.2 Decoding the Fossil Records: Photometric and Spectroscopic Diagnostics 6

1.3 Decoding the Fossil Record: the Tools 8

2 Low-Mass Star Physics 19

2.1 Basic Equations 19

2.2 The Thermodynamical Properties of Low-Mass Stars 30

2.3 Nuclear Energy Production and Nucleosynthesis 40

2.4 Radiative and Conductive Opacity 49

2.5 The Atmosphere Structure 58

2.6 Mass Loss 61

2.7 Diffusion Processes 65

2.8 Rotation 71

2.9 Internal Gravity Waves 75

2.10 Magnetic Fields 77

2.11 Thermohaline Mixing 78

3 From the Main Sequence to the Tip of the Red Giant Branch 83

3.1 Overview 83

3.2 Very Low-Mass Stars 84

3.3 The Main Sequence 94

3.4 The Standard Solar Model 103

3.5 Blue Stragglers 110

3.6 Subgiant Branch Evolution 121

3.7 Red Giant Branch Evolution 123

3.8 The Helium Flash 130

3.9 Theoretical Isochrones for the Hydrogen Burning Stages 134

4 Horizontal Branch and Red Clump 163

4.1 Overview 163

4.2 Mixing Processes 164

4.3 The Horizontal Branch Evolution 169

4.4 Extremely Hot Horizontal Branch and “Blue Hook” Stars 183

4.5 Low-Mass Pulsating Stars in the Core He-burning Stage 189

4.6 Red Clump Stars 206

4.7 The Effects of Non-canonical Processes on HB Evolution 213

5 Asymptotic Giant Branch 231

5.1 Overview 231

5.2 Early Asymptotic Giant Branch Evolution 232

5.3 The Thermally Pulsing Stage 236

5.4 Calibration of Evolutionary AGB Models 254

5.5 Synthetic AGB Stellar Models 257

5.6 Long Period Variables 260

5.7 Nucleocosmochronology 266

5.8 The End of the AGB and Post-AGB Evolution 268

6 White Dwarf Cooling Sequences 275

6.1 General Properties and Simple Models 278

6.2 Detailed Models 280

6.3 Colour-Magnitude Diagrams of WD Populations 294

6.4 Spectroscopic Classification of WDs 300

6.5 Low Mass Co- as He-core WDs 302

7 Resolved Old Stellar Populations in the Galaxy 305

7.1 Introduction 305

7.2 Old Star Cluster Distances 306

7.3 Old Star Cluster Ages 337

7.4 Ages of Old Field Stars from Photometry/Spectroscopy 352

7.5 Empirical Rotation/Activity-Age Relationships 358

7.6 Estimates of the Primordial Helium Abundance 362

7.7 Estimates of the Primordial Lithium Abundance 368

7.8 Multiple Stellar Populations in Galactic Globular Clusters 378

8 Resolved Composite Systems 399

8.1 Synthetic CMD-fitting 400

8.2 Multiple Isochrone-fitting 405

9 Unresolved Old Systems 411

9.1 Building Blocks of a SPSM 415

9.2 Low-Resolution Diagnostics 415

9.3 High-Resolution Diagnostics 455

9.4 Unresolved Composite Systems 473

9.5 Validation of Stellar Population Synthesis Techniques 475

References 481

Index 517