Strong Zeeman effects in the Fe I 5434.5 line observed in a sunspot on August 17, 2024

The Fe I 5434.5 line is widely used as a non-magnetic reference due to its small effective Land'e factor of-0.014. Nevertheless, this line can show significant non-zero Stokes V polarization in active regions on the Sun. In this work, we study the distribution of magnetic fields in the sunspot observed on August 17, 2024 using the high-fidelity Stokes I+V and I-V spectra of three photospheric spectral lines of different magnetic sensitivity: Fe I 5434.5, Ni I 5435.9 and Mn I 5432.5. The observed splitting of the Stokes I plus or minus V bisectors in the Fe I 5434.5 line follows the variation of the corresponding splitting in the two other spectral lines, indicating the presence of a spatial component with an extraordinarily strong magnetic field reaching 22 kG.