European Solar Physics Online Seminar Archive

The physical conditions resulting in the formation and disappearance of penumbral regions are poorly understood. We investigated these conditions by using high-resolution spectropolarimetric observations of a sunspot penumbra from different instruments at ground- and space-based telescopes, namely the SST/CRISP, SDO/HMI, and Hinode/SP. The studied data allowed us to assess the evolution of the magnetic and velocity properties of plasma in the observed region and to analyze the role of several processes found therein. The penumbra forms only on one side of the observed region, characterized by the absence of an overlying magnetic canopy. The penumbra later disappears progressively in time and space. This final evolution of the studied region seems to be governed by the presence of moving magnetic features (MMFs) and of overlying canopies. [more]

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. [more]