Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 59, p. 12-16 (2019)


V. Lozitsky, DrSci

Astronomical Observatory of Taras Shevchenko National University of Kyiv


The main conclusion of our work is that in the greatest sunspot of the active region NOAA 10488 there was a large dispersion of magnetic field strengths, at which the minimum and maximum strengths differed by approximately an order of magnitude. This result applies to the central part of the sunspot umbra, for a square with sides 2 × 2 Mm2 in the picture plane. Observation material was obtained on the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National  University of Kyiv. This instrument allows to analyze the Zeeman effect  simultaneously in thousands of spectral lines of almost the entire visible region of the spectrum. For our analysis, four iron FeI lines with wavelengths of 6290.97, 6301.51, 6302.50 and 6498.97 Ǻ and effective Lande factors 1.481, 1.669, 2.487 and 1.375, respectively, were used. In the studied sunspot, only FeI 6302.5 from these lines has a complete Zeeman splitting, which corresponds to magnetic field of 3400 G. However, the splitting of the other three lines corresponds to magnetic fields in a very wide range, from several hundred Gauss to 3700 G, which indicates significant inhomogeneity of the magnetic field. Also, the shape of bisectors of  I ± V profiles does not correspond to a case of homogeneous field. In particular, theoretically, in a homogeneous and non-longitudinal magnetic field, bisectors should be have the maximum splitting in the nuclei of these lines, whereas in reality the picture is more complicated. All three of these lines show a tendency to increase splitting in distant wings, at distances of 120-250 mAh from their centers. This effect is possible under the two-component structure of the magnetic field (background field + spatially unresolved structures) having magnetic strengths in the range of 4.5-8 kGs in spatially unresolved structures. Magnetic polarity in both components is the same, namely N. The observational data indicate that  the magnetic field value differed significantly not only on the surface, but also in height in the studied sunspot.

Key words
Sun, sunspots, magnetic fields, active region NOAA 10488, Echelle Zeeman-spectrographs, bisectors of profiles of spectral lines, spatially unresolved structures, magnetic field inhomogeneity

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DOI: https://doi.org/10.17721/BTSNUA.2019.59.12-16