| Abstract: | Flare observations in the solar activity complex HR 16862, 16863, 16864 at the end of May 1980 are compared with the structure of force-free magnetic fields calculated from photospheric magnetograph measurements. A series of homologous flares connected with a δ configuration in HR 16864 was possibly caused by a magnetic neutral sheet. The δ configuration consisted of the large preceding spot of HR 16864 and a small satellite of opposite polarity. All magnetic flux from the satellite is connected to the main spot, and at the outer edge of the satellite, away from the main spot, a magnetic neutral sheet is found. This agrees with the observation that all penumbra was situated between parent spot and satellite, which is typical of such † configurations. It is suggested that the flare productivity of these configurations is generally caused by magnetic neutral sheets at the penumbra-free outer boundary of the satellites. |
