He i Vector Magnetic Field Maps of a Sunspot and Its Superpenumbral Fine-Structure
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Advanced inversions of high-resolution spectropolarimetric observations of the He i triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29 January 2012. Multiple atmospheric models are employed in the inversions because superpenumbral Stokes profiles are dominated by atomic-level polarization, while sunspot profiles are Zeeman-dominated, but also exhibit signatures that might be induced by symmetry-breaking effects of the radiation field incident on the chromospheric material. We derive the equilibrium magnetic structure of a sunspot in the chromosphere and furthermore show that the superpenumbral magnetic field does not appear to be finely structured, unlike the observed intensity structure. This suggests that fibrils are not concentrations of magnetic flux, but are instead distinguished by individualized thermalization. We also directly compare our inverted values with a current-free extrapolation of the chromospheric field. With improved measurements in the future, the average shear angle between the inferred magnetic field and the potential field may offer a means to quantify the non-potentiality of the chromospheric magnetic field to study the onset of explosive solar phenomena.
KeywordsMagnetic fields: chromosphere Sunspots: magnetic fields Active regions: magnetic fields
The NSO is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for the National Science Foundation. FIRS has been developed by the Institute for Astronomy at the University of Hawaii jointly with the NSO. The FIRS project was funded by the National Science Foundation Major Research Instrument program, grant number ATM-0421582. We acknowledge the NASA/SDO HMI science team for providing high-quality data. We also extend our gratitude to Andres Asensio Ramos and Andreas Lagg for developing very useful inversion tools for the He i triplet.
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