Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b, receives enough ultraviolet

Understanding stellar structure and evolution significantly impacts our understanding of the tight-knit evolution of galaxies and exoplanet systems. However, hidden behind the luminous layers of the stellar atmosphere, the deep interior of a star is eluding from direct measurements. The seismic study of waves propagating the deep interior provides

We divide this talk into two parts. In the first part, we will introduce the numerical codes we use, mainly in solar physics, to infer information about the solar atmosphere from spectro-polarimetric observations. In particular, we will present a new version that was recently developed (see Ruiz Cobo et al., 2022). In the second part of the talk