ESPOS: Ca II K brightness as a function of magnetic field strength and characteristics of the observations (M. Murabito)

Solar observations have often served as benchmarks of stellar conditions. A particularly illustrative example of the above link is given by the observations in the Ca II K and H lines at 393.367 nm and 396.847 nm, respectively, which are the two deepest and broadest absorption lines in the visible spectrum of the Sun. Although widely observed over the years, several aspects of the emission of these lines are however still not fully understood. This is the case of e.g. the exact relationship between Ca II K emission and magnetic field strength. To the aim of reassessing this relationship, we analyzed state-of-the-art observations of the solar atmosphere obtained at the Swedish Solar Telescope with the CRisp Imaging SPectropolarimeter and with the CHROMospheric Imaging Spectrometer on regions characterized by a different ambient magnetic field. On these observations we analyzed the dependence of the Ca II K line brightness, as well as the relationship between Ca II K emission and magnetic field strength on different surrounding conditions of the solar atmosphere and characteristics of the observations, such as spectral bandwidth and spatial scale. The data and methods employed, and results achieved by our analysis will be presented, with emphasis on their impact on the interpretation of previous findings in the literature and application in future studies.