aat Acta Astrophys. Tau. Acta Astrophysica Taurica 2712-925X Kiselev Nikolai Nikolaevich, Mosсow, settlement Moskovskii, Tat'yanin Park Str., 12, Moscow, Russia. RU 102 Research articles Ultraviolet emission of unipolar active regions and a relation between its intensity and magnetic flux decay rate Plotnikov Andrey Crimean Astrophysical Observatory, Nauchny 298409 22 03 2025 6 1 5 8 12 03 2025 Copyright (c) 2026 Plotnikov A. 2026 Andrey Plotnikov The metadata for this submission is licensed under a Creative Commons Attribution 4.0 International License. Copyright and publishing rights for texts published in Acta Astrophysica Taurica is retained by the authors, with first publication rights granted to the journal.Texts are free to use with proper attribution and link to the licensing (Creative Commons Attribution 4.0 International).

This study uses data on 617 active regions (ARs) acquired by the Solar Dynamics Observatory. Unipolar ARs exhibit a lower density of He II 304 Å ultraviolet (UV) emission above sunspots as compared to the ARs of other types. Bipolar and multipolar ARs, regardless of their magnetic flux, show a similar density of UV emission above sunspots. In contrast, in unipolar ARs, the UV emission density increases with increasing magnetic flux. This relationship can be used to estimate the magnetic flux values from the maps of UV emission density. Additionally, the total unsigned magnetic flux decay rate is in moderate correlation with the UV emission above sunspots. This correlation may help to explain the phenomenon of slow-decaying unipolar ARs.

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