Indications of 8-kilogauss magnetic field existence in the sunspot umbra

We present magnetic field diagnostics in two big sunspot of different magnetic polarity observed on 18 May 2002 and 29 October 2003. In these sunspots, according to visual measurements, magnetic field strength in Fe I 5250.2 Ǻ line was about 3500 gauss. The existence of stronger fields follows from the detailed study of fine spectral effects in I ± V and V profiles of Fe I 6301.5 and 6302.5 Ǻ lines, such as: (a) non-parallelism of bisectors in Fe I 6301.5 line related to distance about ±250 mǺ from the line center, and (b) weak secondary Stokes V peaks on distance, on the average, ±375 mǺ from the Fe I 6302.5 Ǻ center. Consequently, we argue that these peculiarities indicate to the fact that spatially unresolved magnetic fields exist in the sunspot umbra, their strength being about 8 kG. In small structures with such very strong fields magnetic polarity was the same as in the background field of the sunspot umbra, and Doppler velocity is about −1.9 km/s (lifting of plasma).