MAGNETIC-FIELD STRENGTHS IN UMBRAL DOTS

Stokes-V and I spectra of sunspot structures have been observed simult aneously in the lines Fe 6843 and Ca 6103 originating from layers whic h differ by more than 350 km. The Fe line is totally split thus allowi ng to deduce the field strength from the Stokes-I and V profiles. Both splitting values yield a field strength reduction up to 20% in bright er (peripheral) dots at the umbral border. This reduction is not seen in the higher layer where the Ca line originates. The faint (central) dots do not exhibit a field strength difference with respect to their darker surroundings. Using the ratio of pi to sigma depressions of the totally split Fe 6843 line as a measure for the field inclination, th e field lines are found to be essentially flatter in a light bridge th an in its neighbourbood. Flatter fields are also found in some of the peripheral dots. The Doppler shifts of the Fe and of the Ca line devia te significantly from each other but do not show a relation to the umb ral structures.