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--- themis [2025/07/04 16:03] – etienne
+++ themis [2025/09/08 16:58] (current) – etienne
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 <color red >   ** New :** </color>
 [[science:resources | Downloadable posters highlighting recent high-resolution observations of solar active regions by THEMIS]]\\
-[[science:results:ESTFrance2025 | June : Presentation of THEMIS results at the EST France 2025 Workshop in Paris (FR).]] \\
-[[science:results:SF2A2025 | July : Presentation of THEMIS results at the "Journées de la SF2A" in Toulouse (FR).]] \\
 Click for information on: \  \  **[[admin:location| How to reach THEMIS locations]]** \ ; \ **[[admin:contacts| How to contact the THEMIS team]]**
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-== THEMIS image of the month: June 2025 ==
+== THEMIS image of the month: August 2025 ==
-<columns 80% l >
-<html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=science:gallery:protu:solarfilament_meteospace_2025june05.jpg"> <img src="https://www.themis.iac.es/lib/exe/fetch.php?media=science:gallery:protu:solarfilament_meteospace_2025june05.jpg" alt="Solar filament observations on June 5th 2025." style="width: 100%; height: auto;"></a></html> \\
-In June, during an observation campaign lead by researchers from the Paris Observatory (France) and the University of Wroclaw (Poland), THEMIS observed solar filaments. Solar filaments are large magnetised structure of the solar corona confining cold chromospheric-like plasma. Thanks to its specific magnetic structure, solar filaments plasma, of a temperature of about 10 000°K, "hangs" thermally isolated from the million °K solar corona. As this dense and cool plasma absorbs the light emitted from the lower solar layer, the filament appears dark relatively to the background.\\
+=== August 2025 ===
+<columns 100% l 60>
+<html> <a href="https://www.themis.iac.es/lib/exe/fetch.php?media=science:gallery:protu:limbprominenceobservation_20250506_withandwithoutao.jpg
+"> <img src="https://www.themis.iac.es/lib/exe/fetch.php?media=science:gallery:protu:limbprominenceobservation_20250506_withandwithoutao.jpg
+" alt="Prominence Halpha observations at limb: Adaptive Optics comparison" style="width: 100%; height: auto;"></a></html> \\
-The THEMIS observation presented here results from two reconstructed images obtained from two adjacent scans over the solar filament with the THEMIS spectrograph slit. The two scans, which have a 80" range with a 0.5" spatial step, are then stitched together to obtain a larger field of view of about 110"  x 90". Only the reconstructed image in the core of Hα line is displayed here, but THEMIS data allow to sample the full range of the Hα line with a spectral resolution of 4mÅ.\\
-THEMIS high-resolution observations are very complementary to the observations of the [[https://www.oca.eu/fr/lag-physol-projects?option=com_content&view=category&layout=blog&id=295&Itemid=908 | Meteospace/3SOLEIL]] solar surveillance service of OCA/CNRS-INSU, which provide full-Sun high cadence (every 10s) Hα observations, presented on the right panel. \\
-Thanks to its high-resolution, as illustrated in the left panel, THEMIS permits to analyse the filamentary structure of the solar filament and understand its magnetic field thanks to THEMIS polarised measurements. In particular, the magnetic properties of the "barbs" of the filament, the features which extend away from the "spine" (the filament axis), remains ill understood and an active topic of research.
+<newcolumn 40%>
+During the 2025 observation campaign of Brigitte Schmieder and Arek Berlicki, THEMIS targeted a small prominence. Prominence are emitting structures that can be observed at the solar limb, beyond the outer edge of the Sun's disk. Prominences and filaments are two aspects of an unique physical feature: a domain of cold chromosphere like plasma, magnetically confined in the much hotter solar corona. While this structure appears as dark when seen in contrast with the disk, and is then called a filament, it appears bright in contrast to the plane of sky. As a magnetised structure filament/prominence can erupt, releasing plasma and material toward the solar system. Understanding how the magnetic structure them is fundamental to comprehend their stability or lack off.
+THEMIS is mainly a [[technical:mtr2 | scanning spectrograph instrument]], i.e. a very thin slit scans the region of interest, in order to obtain high resolution spectrograms. THEMIS images are thus reconstructed. While scanning, THEMIS is thus very sensitive to the effect of turbulence and the reconstructed image have necessarily a lower resolution that direct imaging. On the other hand, THEMIS can deliver simultaneous images at different wavelength.
+\\
 </columns>
+While adaptive optics can generally be used to significantly improve on disc observations, such as with our own [[technical:tao|Themis AO]], AOs fail when trying to observe over the limb because no structure there can be tracked by the AO. Recently our colleagues of the U.S. National Science Foundation National Solar Observatory and New Jersey Institute of Technology, observed [[https://nso.edu/press-release/new-adaptive-optics-shows-stunning-details-of-our-stars-atmosphere/ | beautiful prominence dynamics]] with the Goode Solar Telescope thanks to their [[https://www.nature.com/articles/s41550-025-02564-0 |new coronal adaptive optics]] in a direct imaging approach.
+At THEMIS, during our 2025 campaign we tried a different approach. While we were scanning a prominence at the limb, we use TAO on an offset region which is close to the limb while still on the disc. TAO is a simple AO which isoplanatic region (region where most of the AO correction is done) is limited. Since the isoplanatic region and the region of scientific interest are far away, the AO correction may be limited at the prominence. We were however very please to see that TAO still provide significant improvements. As can be seen in this image of the month, the turbulence induced motions (in the direction of the slit) which are present when TAO is off, are strongly reduced when TAO is switched on. The limb appears much smoother and the prominence better resolved.