Star-Planet Interactions, livre ebook

The exoplanet revolution that began three decades ago has drastically changed our knowledge of the extra-solar systems. Today, we face an extreme diversity and complexity of these systems that can only be understood through the intimate link that exists between the planets and their host stars. The understanding, characterization, and the detection of the exoplanets has to be made in close collaboration between stellar and planetary physicists. The purpose of the school and this book is to provide an update of our current knowledge in some selected research fields dedicated to the interplay between stars and planets. It aims to prepare scientists for a rich new decade for exoplanets with space missions like the upcoming PLATO and ARIEL and the new instruments on the VLT and the future ELT.

Preface i

Scientific and organising committees ii

Sponsors iii

List of participants iv

I Physics of star-planet magnetic interactions1

1 Introduction 2

1.1 The hot exoplanets population......................... 2

1.2 Observational status of star-planet magnetic interactions ........... 3

2 Magnetic interactions in compact exosystems: overview 4

2.1 Sub- vs Super-alfvénic interaction....................... 4

2.2 Different regimes of sub-alfvénic interactions ................. 6

3 Magnetic interactions in compact exosystems: the Alfvén wings 7

3.1 Pre-requisites on magneto-hydrodynamic waves ................ 7

3.2 The concept of Alfvén wings.......................... 9

3.3 Energetics of Alfvén wings . . . . . . . .. . . . . . . . . . . . . . . . . . . 12

3.4 Angular momentum transfer and the secular evolution of stellar systems . . . 15

4 Conclusions 17

Bibliography 17

II Stellar variability in radial velocity 22

1 Introduction 23

2 From the instruments to radial velocities 24

2.1 Instruments . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 25

2.2 From spectra to radial velocities . . . . .. . . . . . . . . . . . . . . . . . . 25

2.3 Observational strategies . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 26

2.4 Complementary information: chromospheric emission . . . . . . . . . . . . 27

2.5 Effect of stellar variability on exoplanet studies in radial velocity: impact and challenges . . . . . . . . . . . . . . . . . . . . 28

3 Stellar processes contributing to radial velocities 29

3.1 General overview . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 29

3.2 Spot and plage contrasts . . . . . . . . .. . . . . . . . . . . . . . . . . . . 30

3.3 Oscillations . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 32

3.4 The granulation . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 33

3.5 Supergranulation . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 36

3.6 Convective blueshift inhibition in plage .. . . . . . . . . . . . . . . . . . . 37

3.7 Evershed flows . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 38

3.8 Meridional circulation . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 38

3.9 Flares . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 40

4 Approaches to the problem 40

4.1 Mitigating techniques . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 40

4.2 Simulations . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 43

4.2.1 Simulations with 1-2 spots . . . . . . .. . . . . . . . . . . . . . . . 43

4.2.2 Simulations with complex activity patterns . . . . . . . . . . . . . . 44

4.2.3 Simulations of the small or large scale dynamics . . . . . . . . . . . 50

4.3 Stellar observations: simultaneous campaigns . . . . . . . . . . . . . . . . . 50

4.4 Observations of the Sun as a star . . . . .. . . . . . . . . . . . . . . . . . . 50

5 Conclusion 51

Bibliography 52

III Stellar activity and transits 65

1 Introduction 66

2 Solar and stellar activity observations 67

3 High precision photometry 68

3.1 Stellar rotation periods . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 69

3.2 Stellar surface reconstruction . . . . . .. . . . . . . . . . . . . . . . . . . . 71

3.3 Stellar differential rotation and star spot evolution . . . . . . . . . . . . . . . 72

4 Planetary transits and stellar activity features in photometry 73

4.1 Effect of non-occulted activity features on the transit depth . . . . . . . . . . 74

4.2 Effect of occulted activity features . . .. . . . . . . . . . . . . . . . . . . . 75

5 Starspots and faculae in transmission spectroscopy 77

6 Effects on other transit parameters 80

7 Planetary transits and stellar granulation 84

7.1 Effect on measured stellar parameters . . .. . . . . . . . . . . . . . . . . . 84

7.2 Effect on transit parameters . . . . . . .. . . . . . . . . . . . . . . . . . . . 84

8 Conclusions 86

Bibliography 87

IV High resolution spectroscopy for exoplanetcharacterisation 103

1 Introductory concepts 104

1.1 The underlying scientific questions . . . .. . . . . . . . . . . . . . . . . . . 104

1.2 Resolution vs Resolving Power . . . . . . .. . . . . . . . . . . . . . . . . . 106

1.3 Using spectroscopy to find exoplanets . . .. . . . . . . . . . . . . . . . . . 107

1.4 Exoplanets and their orbits . . . . . . . .. . . . . . . . . . . . . . . . . . . 108

1.5 Spectroscopy of transiting exoplanets . . .. . . . . . . . . . . . . . . . . . 109

1.5.1 Transmission spectroscopy . . . . . . . .. . . . . . . . . . . . . . . 109

1.5.2 Information from secondary eclipses: reflected light . . . . . . . . . 112

1.5.3 Information from secondary eclipses: thermal emission . . . . . . . . 113

1.5.4 Information from the whole orbit: phasecurves . . . . . . . . . . . . 114

2 High-resolution spectroscopy of exoplanets115

2.1 Key characteristics . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 115

2.2 The signal-to-noise formula and cross correlation . . . . . . . . . . . . . . . 116

2.3 Understanding the analysis of high-resolution exoplanet spectra . . . . . . . 118

2.4 Molecular and atomic species detected . . .. . . . . . . . . . . . . . . . . . 122

2.5 Thermal inversion layers . . . . . . . . .. . . . . . . . . . . . . . . . . . . 123

2.6 From demonstration to comparative exoplanetology . . . . . . . . . . . . . . 124

2.7 Follow-up of TESS exoplanets . . . . . . .. . . . . . . . . . . . . . . . . . 126

2.8 Cloudy atmospheres at high spectralresolution . . . . . . . . . . . . . . . . 127

3 The star as a source of astrophysical noise129

3.1 Stellar spectra are non-stationary . . . .. . . . . . . . . . . . . . . . . . . . 130

3.2 Stellar cross-correlation noise in day-side observations of exoplanets . . . . . 131

3.3 Stellar spectra are distorted during transit . . . . . . . . . . . . . . . . . . . 131

3.4 Modelling the background stellar spectrum .. . . . . . . . . . . . . . . . . 133

3.5 Stellar modelling to accurately measure exoplanet winds and rotation . . . . 135

4 Estimating significance and error bars 137

4.1 The signal-to-noise approach . . . . . . .. . . . . . . . . . . . . . . . . . . 137

4.2 The Welch t-test . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 138

4.3 Estimating the “model” cross correlation function . . . . . . . . . . . . . . . 139

4.4 Bayesian analysis on high-resolution spectra . . . . . . . . . . . . . . . . . . 140

4.4.1 Combining low- and high-resolution spectroscopy . . . . . . . . . . 141

5 Bridging the gap towards habitable planets141

5.1 Planets around M-dwarf stars . . . . . . .. . . . . . . . . . . . . . . . . . . 141

5.1.1 Detecting oxygen in planets around M-dwarfs . . . . . . . . . . . . . 143

5.1.2 Challenges in M-dwarf observations . . .. . . . . . . . . . . . . . . 143

5.2 Combining spectral and spatial resolution .. . . . . . . . . . . . . . . . . . 144

Bibliography 145

V Stellar Winds and Planetary Atmospheres 154

1 Introduction 155

2 Stellar rotation and activity evolution 158

2.1 The observational picture . . . . . . . . .. . . . . . . . . . . . . . . . . . . 158

2.2 The epochs of rotational evolution . . . .. . . . . . . . . . . . . . . . . . . 160

2.3 Activity and rotation . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 161

2.4 Activity evolution . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 163

3 Properties and Evolution of Stellar Winds 164

3.1 Observational constraints on winds . . . .. . . . . . . . . . . . . . . . . . . 164

3.1.1 Rotational evolution . . . . . . . . . .. . . . . . . . . . . . . . . . 164

3.1.2 Radio observations . . . . . . . . . . .. . . . . . . . . . . . . . . . 166

3.1.3 Interactions with the interstellar medium. . . . . . . . . . . . . . . 166

3.1.4 Effects on planetary companions . . . . .. . . . . . . . . . . . . . . 168

3.2 Solar wind: basic properties . . . . . . .. . . . . . . . . . . . . . . . . . . 168

3.3 Wind physics . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 171

3.4 Winds of active stars . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 172

3.5 Coronal mass ejections . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 174

4 Earth’s Upper Atmosphere and Wind Interactions 174

4.1 The vertical structure of the Earth’s atmosphere . . . . . . . . . . . . . . . . 175

4.2 Exospheres, magnetospheres, and winds . . .. . . . . . . . . . . . . . . . . 177

5 Planetary Upper Atmospheres and Escape 179

5.1 Hydrodynamic escape . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 180

5.2 Upper atmospheres and active stars . . . .. . . . . . . . . . . . . . . . . . . 182

5.3 The importance of atmospheric cooling . . .. . . . . . . . . . . . . . . . . 184

5.4 The importance of the star’s rotational evolution . . . . . . . . . . . . . . . . 184

5.5 Stellar winds, CMEs, and habitable zone planets . . . . . . . . . . . . . . . . 186

6 Discussion 187

Bibliography 188

VI Main ways in which stars influence theclimate and surface hab[1]itability of theirplanets 202

1 Introduction 203

2 Influence of the bolometric emission distribution on the climate 205

3 Influence of the UV emission on the photochemistry 208

4 Influence of the X-EUV emission on atmospheric loss 209

5 Influence of the temporal evolution of the stellar emissions 210

6 Conclusions 211

Bibliography 212