ANOMALOUS WIDENING OF 5434.5 LINE IN SUNSPOTS: SUPER-STRONG MAGNETIC FIELDS?

Abstract

We present results of spectralobservations of two sunspots in six metal lines near Fe I5434.5 A, which have effective Lande factors g eff from –0.014 to 2.14. The observations were made on July 8 andAugust 25, 2015, with the ATsU-5 telescope of GAO NASof Ukraine using a circular polarization analyzer andspectra registration with the SBIG ST-8300 CCD camera.The following line parameters are compared: observedsplitting of I ± V profiles, the width and depth of the StokesI profiles. Significant differences of the measured magneticfield strengths B eff were found in separate places of thespots and by lines with different g eff values. The Fe I 5434.5Ǻ line (g eff = –0.014) shows measurable splitting in somelocations of the sunspots, which corresponds to themagnetic field B obs ≈ 20 kG. Comparison of the widths anddepths of the line profiles revealed several special places inthe sunspots, where the Fe I 5434.5 Ǻ line was expandedadditionally by ≈ 15–35%, whereas other lines with largerLande factors did not have such a feature. One of thereasons for this expansion could be a sharp and localincrease of turbulent velocities, but no active processes suchas solar flares or significant Doppler flows were observed atthese locations. A semi-empirical model constructed for thefirst sunspot by FeI 5434.5 line using inverse code withTikhonov`s stabilizers shows an anomalous feature – themaximum of microturbulent velocities in the upperphotosphere and the temperature minimum zone instead ofthe usual small increase of microturbulence at these heights.This may be the effect of very strong magnetic fields ofmixed polarity or unresolved turbulent structures. As to firstcase, the estimated value of the magnetic field in suchlocations of sunspots is ~10 5 G, which requires additionalcareful verification.