Observational Techniques with Transiting Exoplanetary Atmospheres

Transiting exoplanets provide detailed access to their atmospheres, as the planet’s signal can be effectively separated from that of its host star. For transiting exoplanets three fundamental atmospheric measurements are possible: transmission spectra—where atmospheric absorption features are detected across an exoplanets limb during transit, emission spectra—where the day-side average emission of the planet is detected during secondary eclipse events, and phase curves—where the spectral emission of the planet is mapped globally following the planet around its orbit. All of these techniques have been well proven to provide detailed characterisation information about planets ranging from super-Earth to Jupiter size. In this chapter, I present the overall background, history and methodology of these measurements. A few of the major science related questions are also discussed, which range from broad questions about planet formation and migration, to detailed atmospheric physics questions about how a planet’s atmosphere responds under extreme conditions. I also discuss the analysis methods and light-curve fitting techniques that have been developed to help reach the extreme spectrophotometric accuracies needed, and how to derive reliable error estimates despite limiting systematic errors. As a transmission spectra derived from primary transit is a unique measurement outside of our solar system, I discuss its physical interpretation and the underlying degeneracies associated with the measurement.