THEMIS Solar Telescope

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.

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 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.