Abstract
Complete photoelectric spectra of the photosphere as well as of both umbra and penumbra of a typical sunspot, ranging from 3900–8000 A, have been obtained at the Locarno observatory. An automatic scanning device, a high precision electronic divider and an on-line Oscillomink penless recorder enabled us to eliminate the noise produced by image distortion and to scan the entire visible spectrum within just 5 h. The recordings have a linear dispersion of about 50 mm/A and a spectral resolution of 40 mA or better. Simultaneously with these observations the momentary continuous spot intensity and its fast variation with time due to seeing variations have been recorded with a frequency resolution up to 100 Hz. In order to provide as much data as possible for the correction of the umbral spectrum for parasitic light, we also measured the limb profile and the aureola intensity at several wavelengths.
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