Speaker
Description
The Sunrise Ultraviolet Spectropolarimeter and Imager (SUSI) instrument captured high spectral and spatial resolution observations of the strong Fe I line at 407.17 nm. We observe that within a sunspot penumbra, this line displays multi-lobed Stokes V profiles unlike other lines in the same spectrum. These multi-lobed profiles were predicted in earlier computations and are found to result from the bell-shaped Stokes I profiles of this line within the penumbra. The multi-lobed Stokes V profiles are best seen in the inner parts of the penumbra, where the Stokes V signal of the line is stronger, and the Stokes I line shape displays the characteristic flattening of the inner wing along with a steep line core. This allows us to measure magnetic field strengths at different heights in the atmosphere by applying the weak-field approximation to the line core and line wing separately. The LOS magnetic field strengths we obtain are, as expected above the inner penumbra and magnetic elements, stronger in the photosphere than higher up. Despite the blend line in the blue wing and the relatively weak Stokes V signals when compared with other lines, the Fe I 407.17 nm line could be used as an initial estimate of the magnetic field at two different height ranges, for example for initializations of inversions.