How does the radiative environment affect the chemistry of exoplanet atmospheres?

The high-energy radiation environment of exoplanets can greatly affect their atmospheric chemistry through photo-chemical reactions and ionisation of the upper parts of the atmospheres. In order to analyse the chemistry of exoplanet atmospheres, it is therefore necessary to understand the radiative environment the planet is placed in and what effects it has on the atmosphere.  The aim of this project is to study how the chemistry of exoplanet atmospheres is affected by the radiative environment. We focus on three different sources of high-energy radiation; the XUV radiation of the host star, the stellar energetic particles (SEPs) of the host star, and the galactic cosmic rays (GCRs) originating from outside the planetary system. We model the disequilibrium chemistry of a gas giant test planet, using the chemical kinetic network, STAND2020, coupled to the 1D photo-chemistry and diffusion code, ARGO. The radiative sources are introduced in the models as spectral energy distributions for the XUV radiation, and as ionisation rates for for the SEPs and GCRs. STAND2020 excels by its complexity in H/C/N/O chemistry which allows us to study the effect of the irradiation on larger complex molecules such as prebiotic molecules and haze precursors.  In this talk, we present a grid of models run for host stars of the types; O,B,A,F,G,K, and M, under varying influxes of GCRs. For each of the stellar spectral types a representative spectra, combined from observations and models, has been chosen from a comprehensive search of recent literature. The SEP flux for each stellar type is approximated from the stellar activity by scaling the solar SEP spectrum based on observations of X-ray flares. The GCR flux is varied step-wise from no GCRs (representative of a system that is highly shielded by the heliosphere of an active host star) to GCR fluxes estimated for the ISM in the central part of the galaxy (representative of a system in a highly radiative galactic environment with a weak heliosphere of a quiet host star). This grid over radiative environments allows us an insight into the effects of high-energy radiation on atmospheric chemistry, and can help guide our analysis of exoplanet atmosphere observations based on the stellar type of the host star and the environment the system is located in.