Stokes I, Q, and U spectra of three DUs extracted from the source region with background subtraction (denoted in Figure 1). The three Stokes I spectra (DU1 in black, DU2 in red, DU3 in green) are shown in the upper panel. The six Stokes Q spectra (DU1 in black, DU2 in red, DU3 in green) and U spectra (DU1 in blue, DU2 in light blue, DU3 in magenta) are displayed in the middle panel. It appears that only two model lines (for Q and U spectra) are visible in this panel because the differences between the model lines for the three DUs are too small to be shown. The lower panel shows the fit residuals as (data − model)/ error.