We performed full Stokes spectropolarimetric observations of loop footpoints in the active region NOAA 13363 during a C-class flare with the GREGOR Infrared Spectrograph (GRIS) on 2023 July 16. The observed spectral region included the photospheric Si I 10 827 A and Ca I 10 839 A lines and the chromospheric He I 10 830 A triplet. Simultaneously

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

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