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The observational set-up for a detailed study of the velocity, intensity and magnetic-field fine structure in and around a sunspot is described. On highly resolved spectra we detected in the vicinity of a sunspot a large number of points with strong magnetic fields (magnetic knots).

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Low noise photoelectric measurements of the line profile of the g = 0 Fe line 2 5576.097 combined with determinations of the wavelength shift of its centre calibrated by use of an 12 absorption tube are reported. Measurements taken at various limb distances (1.0 < cos ~ < 0.2) and along 4 different diameters of the Sun are used to investigate the behaviour of the line asymmetry (C-shape) and wavelength shift of the line centre as functions of cos 0 and of latitude and to search for possible pole-equator differences.An accuracy of approx. 0.8 mA r.m.s, is achieved for the determination of the centre of the solar line relative to the iodine lines and of 0.3 mA to 1 mA r.m.s, for the relative variations of the C-shape. The analysis shows a significant difference between the limb-effect curves along polar and equatorial diameters for cos ~ < 0.4 and changes of the C-shape for 0.9 > cos ~ > 0.6 with a rather strong indication of a latitude dependence of the C-shape. This latitude dependence may account for the so-called 'ears' observed by Howard et al. (1980) who used the well-known Doppler compensator method which integrates the line asymmetry from the line wings to the core.