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Wide-Field Image Restoration of G-Band and Ca ii K Images Containing Large and Complex Active Regions

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Abstract

Restoration of solar images to achieve near diffraction-limited spatial resolution is commonly implemented on large-aperture solar telescopes. However, the extent of the restored field-of-view is typically only 100′′ or even smaller. This study reports on wide-field image restoration of G-band and Ca ii K images obtained with the 0.7-meter Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain. The Kiepenheuer Adaptive Optics System (KAOS) at the VTT provides a field-of-view with a diameter of 270′′. Time series of datasets with 100 images were acquired with a large-format (7920 × 6004 pixels) CMOS imager at a frame rate of 30 Hz. An experimental optical setup that enabled wide-field imaging is briefly presented. Results from speckle-masking imaging and Multi-Frame Blind Deconvolution (MFBD) demonstrate the unique potential of the VTT for wide-field imaging. Power spectral analysis quantifies the instrument performance as a function of time and with distance from the lock point of the AO system. Further science capabilities are established using Local Correlation Tracking (LCT), Background-subtracted Solar Activity Maps (BaSAMs), and image quality/seeing metrics. In summary, commercial off-the-shelf camera systems can become an asset to sub-meter-class solar telescopes and open up new science opportunities at the interface between large-aperture and synoptic solar telescopes.

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Data Availability

No datasets were generated or analysed during the current study.

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Acknowledgments

The Vacuum Tower Telescope (VTT) at the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias is operated by the German consortium of the Institut für Sonnenphysik (KIS) in Freiburg, the Leibniz-Institut für Astrophysik Potsdam (AIP), and the Max-Planck-Institut für Sonnensystemforschung (MPS) in Göttingen. This research has made use of NASA’s Astrophysics Data System (ADS). DeepL Write was used in copy editing (spelling, grammar, and readability) of the manuscript. We would like to thank the referee for very valuable and substantial comments, which helped to significantly to improve the manuscript.

Funding

This study was supported by grants KO 6283/2-1 and VE 1112/1-1 of the Deutsche Forschungsgemeinschaft (DFG). AP received funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation program (grant agreement No. 833251 PROMINENT ERC-ADG 2018).

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Authors and Affiliations

  1. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482, Potsdam, Germany

    Robert Kamlah, Meetu Verma, Carsten Denker, Ioannis Kontogiannis, Alexander G. M. Pietrow, Jürgen Rendtel, Emily Lößnitz & Arooj Faryad

  2. Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24 – 25, 14476, Potsdam, Germany

    Robert Kamlah, Emily Lößnitz & Arooj Faryad

  3. Eidgenössische Technische Hochschule Zürich, Wolfgang-Pauli-Str. 27, 8093, Zürich, Switzerland

    Ioannis Kontogiannis

  4. Faculty of Informatics, Università della Svizzera italiana, Istituto ricerche solari Aldo e Cele Daccò (IRSOL), 6605, Locarno, Switzerland

    Ioannis Kontogiannis

  5. Center for Mathematical Plasma Astrophysics, Deptartment of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001, Leuven, Belgium

    Alexander G. M. Pietrow

  6. Institut für Sonnenphysik (KIS), Georges-Köhler-Allee 401a, 79110, Freiburg, Germany

    Reiner Volkmer, Rolf Schlichenmaier, Thomas Berkefeld, Miguel Esteves & Olivier Grassin

  7. Thüringer Landessternwarte Tautenburg (TLS), Sternwarte 5, 07778, Tautenburg, Germany

    Markus Roth

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Contributions

The individual contributions by the authors are listed according to the Contributor Roles Taxonomy (credit.niso.org). Robert Kamlah: formal analysis, investigation, software, validation, visualization, and writing – original draft; Meetu Verma: formal analysis, investigation, project administration, software, supervision, validation, visualization, and writing – review & editing; Carsten Denker: conceptualization, data curation, formal analysis, investigation, project administration, software, supervision, validation, visualization, and writing – review & editing; Ioannis Kontogiannis: investigation and writing – review & editing; Alexander G. M. Pietrow: investigation and writing – review & editing; Jürgen Rendtel: investigation and writing – review & editing; Emily Lößnitz: investigation and writing – review & editing; Arooj Faryad: investigation and writing – review & editing; Reiner Volkmer: project administration – review & editing; Rolf Schlichenmaier: project administration – review & editing; Thomas Berkefeld: resources – review & editing; Miguel Esteves: resources – review & editing; Olivier Grassin: resources – review & editing; Markus Roth: project administration – review & editing

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Kamlah, R., Verma, M., Denker, C. et al. Wide-Field Image Restoration of G-Band and Ca ii K Images Containing Large and Complex Active Regions. Sol Phys 300, 62 (2025). https://doi.org/10.1007/s11207-025-02472-6

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