Paper detail

Absolute shifts of Fe I and Fe II lines in solar active regions (disk center)

We estimated absolute shifts of Fe I and Fe II lines from Fourier-transform spectra observed in solar active regions. Weak Fe I lines and all Fe II lines tend to be red-shifted as compared to their positions in quiet areas, while strong Fe I lines, whose cores are formed above the level $\log τ_5\approx-3$ (about 425 km), are relatively blue-shifted, the shift growing with decreasing lower excitation potential. We interpret the results through two-dimensional MHD models, which adequately reproduce red shifts of the lines formed deep in the photosphere. Blue shifts of the lines formed in higher layer do not gain substance from the models.