Host stars and their effects on exoplanet atmospheres: Reconstructing the missing extreme-ultraviolet and Lyman-alpha radiation that exoplanets see

Abstract Whether an exoplanet can retain its atmosphere is mainly controlled by the extreme-ultraviolet (EUV) radiation received from its host star, and the photo-chemistry in its outer atmosphere is driven by the far-ultraviolet radiation, primarily the hydrogen Lyman- α line, from its host star. Since interstellar hydrogen absorbs most of this EUV and Lyman- α radiation, there is a critical need for accurate reconstruction techniques to identify the intrinsic EUV and Lyman- α radiation that impacts the outer atmosphere of an exoplanet. This paper describes and critiques the available reconstruction techniques.