Exoplanetary transmission spectra with the MARCS code

Exoplanetary atmospheres’ physical and chemical structure are influenced by the irradiation from the host star. The study of their properties allows to determine the conditions for the habitability of an exoplanet. The physical and chemical properties can be determined through the transmission spectrum, i.e. the spectrum observed during the transit of the planet in front of its host star. Currently, transmission spectra are obtained by measuring the variation in the transit depth at different wavelengths. A more accurate approach is to calculate the pressure-temperature structure of the atmosphere and the continuum absorption, scattering and line opacities and use these information to propagate the light inside the atmosphere to the observer. A few groups have done this, e.g. Molliére et al 2017. This work aims to model the transmission spectrum by calculating the transmission of stellar light through atmospheric annuli in transit geometry. The atmospheric model is calculated with the MARCS code (Gustaffson et al 2008), which is a 1D, fast, self-consistent, stellar atmospheres modelling tool that integrates stellar structure, chemical equilibrium and radiative transfer equations. It has been adapted to model irradiated atmospheres. The code produces 1D models of the day-side and night-side of giant gaseous planets that are then combined and used to produce the transmission spectrum.