TRANSITING EXOPLANETS

Transcription

1 TRANSITING EXOPLANETS Introduction 11 Chapter 1 Our Solar System from afar 13 Introduction Direct imaging Coronagraphy Angular difference imaging Astrometry Radial velocity measurements The stellar reflex orbit with asingle planet Reflex radial velocity for many non-interacting planets Transits Transit depth for terrestrial and giant planets Geometric probability of atransit Microlensing 42 Chapter 2 Exoplanet discoveries by the transit method 47 Introduction The hot Jupiters, STARE,and HD b, the first transiting exoplanet Howmany transiting planets will asurvey find? N(S) for standard candles of uniform space density The duration ofanexoplanet transit The signal-to-noise ratio Survey volume and number ofstars searched The number oftransiting planets per star Scaling laws forthe discovery of transiting exoplanets Estimating the expected planet haul Wide-field astronomy Design considerations and hardware Issues arising from wide-area coverage From images to light curves TheSuperWASP archive Transit search methods Astrophysical mimics 79 5

2 2.7.1 Blended eclipsing binary systems Grazing eclipsing binary systems Transits by planet-sized stars Candidate winnowing and planet confirmation Follow-up observations Tests performed on the survey photometry Spectroscopic confirmation of candidates Thepregnant pause: overcoming systematic errors 84 Chapter 3 What the transit light curve tells us 90 Introduction Kepler s third law and exoplanet orbits The semi-major axis The orbital speed The orbital inclination, the impact parameter and the transit duration Theshape of the transit light curve Limbdarkening The eclipsed area as afunction oftime The light lost from an axially symmetric stellar disc Theanalytic underpinnings of transit light curve fitting The scale of the system The radii and consistency checks The orbital inclination and the mass of the planet Parameter determination from transit light curve fitting Light curve features to be matched The process of light curve fitting Chapter 4 The exoplanet population 122 Introduction Selection effects Direct imaging Astrometry Radial velocity Transits Microlensing Thedemographics of the known exoplanets Known population as afunction ofdiscovery method 126

3 4.2.2 The radial velocity planets The transiting exoplanets Thestructure of giant planets The underlying physics The equation ofstate The virial theorem and the contraction and cooling of giant planets Parameters governing the size of agiant planet Core mass Total mass Age and irradiation Metallicity Tidal heating Themass radius diagram Densities of transiting exoplanets Compositions of transiting exoplanets Surface gravities of transiting exoplanets What can we say about the Galaxy s population of planets? 159 Chapter 5 Transmission spectroscopy and the Rossiter McLaughlin effect 164 Introduction The equilibrium temperature Transmission spectroscopy Atmospheric transparency and clouds The first detection ofanexoplanet s atmosphere HD b s transit in Lyman α OI and CII absorption during HD b s transit An alternative explanation of the Lyman α absorption Rayleigh scattering in HD b the sky is blue COand H 2 Owith Spitzer Na D absorption from HD b: the first ground-based atmosphere detection What next? The Rossiter McLaughlin effect Spin orbit angle and the projected spin orbit angle Analysis ofthe Rossiter McLaughlin effect 184 7

4 5.3.3 Comparison of the amplitudes of the orbital radial velocity and the Rossiter McLaughlin effect Results from Rossiter McLaughlin observations 189 Chapter 6 Secondary eclipses and phase variations 194 Introduction Expectations using simple approximations Reflected starlight Day side and night side equilibrium temperatures Ratio of star and planet fluxes atsecondary eclipse Peak to trough amplitude of the orbital light curve Contrast units and flux units Caveats on these expectations Secondary eclipses The first detections The Kepler mission The emergent spectrum: exoplanets with and without hot stratospheres Orbital eccentricity Phase curves 212 Chapter The 24 µm phase curve of υandb,a non-transiting hot Jupiter The 8 µm phase curve and amap of HD b 214 Transit timing variations and orbital dynamics 219 by Andrew Norton Introduction Newton s law of gravity Two bodies Orbits Three bodies Solving the equations of motion Theshapes oforbits Circularization oforbits Increasing the eccentricity of orbits The effect of eccentricity on the detectability of transits Orbital dynamics of known exoplanetary systems 232 8

5 7.3.1 Exoplanets in habitable zones Multiple exoplanet systems Exoplanets in multiple star systems Transit timing variations due to another planet Interior planets on circular orbits Interior planets on eccentric orbits Exterior planets Transit timing variations for planets in resonant orbits Exomoons Transit timing variations and transit duration variations due to exomoons The stability ofthe orbit of an exomoon Exotrojans The orbits ofexotrojans Transit timing variations due to exotrojans Theformation, evolution and migration ofplanets 250 Chapter 8 Brave new worlds 255 Introduction Future searches for transiting planets Kepler: the future begins now! Wide-field surveys in space MEarth: transiting exoplanets around nearby Mdwarf stars Characterization ofterrestrial transiting exoplanets Spectroscopy with the James Webb Space Telescope Confirmation of terrestrial transiting planet candidates Life in the Universe Habitability The habitable zone What makes ahabitable planet? Class I,II, III and IVhabitable planets Habitable worlds and biomarkers Conclusions 271 References and further reading 273 Appendix 281 9

6 Solutions 284 Acknowledgements 324 Index