Salvo Luigi Guglielmino, Mariachiara Falco, Mariarita Murabito

We describe high-resolution observations of a GOES B-class flare observed at the Dunn Solar Telescope with IBIS and ROSA instruments. The flare was characterized by a circular ribbon at chromospheric level and was interpreted as a consequence of a magnetic reconnection event that occurred at a three-dimensional (3D) coronal null point located above a supergranular cell. We highlight some interesting observational aspects that need to be explained by models. We observe a bundle of loops corresponding to the outer spine that becomes brighter a few minutes before the onset of the flare. The circular ribbon was formed by several adjacent compact kernels with a size of 1″–2″ and brightening sequentially in clockwise direction. We note that the kernels with a stronger intensity emission were located at the outer footpoint of the darker filaments, departing radially from the center of the supergranular cell. The site of the 3D null point and the shape of the outer spine were also detected by RHESSI in the low-energy channel between 6.0 and 12.0 keV. We ascribe the low intensity of the flare to the low amount of the involved magnetic flux and to its symmetric magnetic configuration.

P. Costa, I. Ermolli, F. Giorgi, S.L. Guglielmino, M. Murabito, M. Oliviero, G. Viavattene

We describe the ongoing upgrade of the INAF small telescopes providing full-disc observations at various bands of the visible spectrum of the Sun, specifically of the Catania, Rome-PSPT, and VAMOS telescopes. The acquisition system of the former has been updated to provide observations in the Hα line with pixel scale of 1” and cadence up to 24 images per sec, whose quality and format allow easy exploitation of the Lucky-imaging and flare detection techniques developed within the SPRING project. The update of the control system of the PSPT is also under study to ensure the continuation of the time series of Ca II K and continuum observations started 25 years ago. Finally, the opto-mechanical layout of the VAMOS telescope has been revised to improve the spatial resolution of the Dopplergrams, magnetograms, and intensity images obtained with potassium MOF cells at a 25 cm aperture telescope.