The flare of December 17, 1980 observed with high time resolution by a digital CCD camera

Abstract

An electro-optical system for the digital registration of Hα-images with high time resolution (1.6 s) is described. The sensor is a Charge-Coupled-Device (CCD) with 100 × 100 elements, resulting in our case in a resolution of 3 × 4″ on the Sun. Data are digitized with a resolution of 8 bit and written on magnetic tape by means of a minicomputer. Image analysis on a large computer eliminates instrumental effects, calibrates the data and reproduces them in graphical form. The analysis of a first flare (December 17, 1980; 12:09 UT) shows that the different flare kernels brighten at different times and pulsate in diameter and intensity. The decay of the flare is slower if fainter regions are included. This supports the idea that an impulsive flare confined in a magnetic loop spreads out over a larger area during the gradual phase. Comparison with microwave observations shows the same risetime for both spectral ranges which indicates that they are excited by the same agent. Furthermore the Hα-flare lags the microwave burst by about 8 s indicating that the source of primary energy release lies above the Hα emitting layers.