Evaluation of a Magnetic Field Inversion Method Using Only Stokes I

Ali, Abduhla; Diercke, Andrea; Hofmeister, Stefan; Kuckein, Christoph; Savin, Daniel Wolf; Hahn, Michael
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Research Notes of the American Astronomical Society

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We compare a method for inferring the photospheric vector magnetic field using only spectroscopy to a conventional method based on polarimetry. The magnetic field strength B and inclination angle can be inferred from the Zeeman splitting using only Stokes I. We applied this method to a sunspot observed with the Vacuum Tower Telescope and compared the results to vector magnetograms from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory, which used a polarimetric inversion. The spectroscopic inversion tends to show higher values in B compared to the polarimetric data. In quiet regions the discrepancy in B was typically a factor of two. In the strong sunspot fields, the differences averaged ≈22%. These discrepancies are significant, but comparable to those typically found among magnetograms from different instruments. Our results support the use of the spectroscopic inversion technique to provide a fast and reasonable estimate of B.