Peculiarities of the Zeeman splitting in lines with small Lande factors in a sunspot spectrum

Abstract

The Zeeman splitting of FeI 6093.66, 6094.419, 5436.3 and 5436.6 Å lines is studied using I±V Stokes profiles related to a big sunspot observed of 25 March 1991 on Echelle spectrograph of horizontal solar telescope of Astronomical Observatory of Kyiv Taras Shevchenko University. Measurements in lines FeI 5436.3 and 5436.6 with relatively large Lande factors (g=1.44 and 1.82, respectively) shown, that magnetic field in sunspot umbra was in range 1.4–1.6 kG and had S polarity. However, it was found that lines FeI 6093.66 and 6094.419 with small and opposite Lande factors (g=0.33 and –0.22) have magnetic splitting of the same sign, i.e. second line indicates opposite magnetic polarity, namely N. An analysis of probable causes of this effect allows to conclude the possible influence of the Pashen–Back effect in presence of very strong fields of ∼ 10^5 G. In case of such “superstrong” fields, one can expect the Zeeman effect manifestations in other lines with smallest Lande factors. In fact, similar spectral perturbations (like very small Zeeman splitting) were found in FeI 5434.5 line (g = -0.014). It was shown, that this splitting is maximum in line core (where it reachs 3–5 mÅ) and decreases, in general, from line core to wings. Corresponding low magnetic strength limit of longitudinal field is about 10–13 kG. Perhaps, such fields were placed in subtelescopic magnetic structures embedded in more weak background field of sunspot umbra.

Keywords

• Zeeman splitting in spectral lines
• solar magnetic fields