Bernard Gelly

THEMIS, the French 1-m class solar telescope, has benefited from profound renovations and modification of its light path over the last 10 years. Thanks to a state-of-the art solar adaptive optics, THEMIS observations can now reach the diffraction limit at 0.15”, enabling to resolve details on the scale of 100 km on the Sun. In the last two years, THEMIS spectro-polarimetric mode has also been renewed and tested. Unprecedented observations are thus now being obtained by THEMIS. Upcoming evolutions of THEMIS, such as the reception and commissioning of a new synergic instrument, the renewed Italian “Interferometric BIdimensional Spectrometer (IBIS 2.0)” will also be discussed.

T. Berkefeld, A. Asensio Ramos, C. Kuckein, M. Esteves Perez, J. C. Trelles Arjona, M. Collados and KIS workshop team

Adaptive Optics (AO) developments enable new high-resolution solar observations, particularly near the solar limb where conventional systems face limitations. At the 1.5-m GREGOR telescope, a novel Hα-sensitive Wave Front Sensor (WFS) developed by KIS allows stable AO correction using chromospheric intensity structures, even off-limb in prominences. We present first performance results from the science verification campaign, combining Hα imaging from BBI and spectropolarimetry from GRIS. The results show improved image stability and correction quality, confirming the system’s potential for future limb and chromospheric studies.

Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, which enables key spectral lines (e.g., Ca II H/K, H$\beta$ , Sr II, Na I D1/D2, etc.) to be studied, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming 2m class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny-Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding 20 per second possible while operating in a non-polarimetric configuration. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research.

Image restoration with MFBD methods, current status and possible future development. (Movies showing anisoplanatism missing from slides.)

M. Löfdahl, J. de la Cruz Rodríguez, B. Lindberg, J. Leenaarts, H. Socas-Navarro

We discuss how to optimise the science output of the European Solar Telescope (EST), when used without the wide-field compensation for high-altitude seeing that the EST multi conjugate adaptive optics (MCAO) will offer. This will likely be the mode of operating EST during its first year, following first light. In this mode, the spatial resolution of a much smaller telescope could surpass that of EST. We propose to operate EST in multi-aperture mode, which will, together with the use of short exposure times and image reconstruction techniques, dramatically improve image quality. In particular, the multi-aperture mode will provide the sustained stable high image quality needed for obtaining time sequences of spectropolarimetric data. The multi-aperture mode is implemented by optically segmenting the 4.2 m aperture into six 1.4 m subapertures by a low-cost modification of the camera lenses of the three Fabry-Perot systems that are expected to be operational soon after first light.

This presentation discusses system polarimetry approachs at DKIST. It covers methods and lessons for large-aperture solar spectropolarimetry.

Spectrum restoration combines the benefits of grating spectrographs, an excellent spectral fidelity and a potentially wide spectral range, with the high angular resolution achievable with filter-based imaging instruments. The method is used with ground-based telescopes and has also been implemented for the SUSI instrument aboard Sunrise 3. This contribution briefly introduces the method and the benefits for the science, but focuses on the lessons learned from a series of setups that have been deployed to ground-based solar telescopes in the past. The insights gained from success and failure of those endeavors were condensed into the distinct concept and the design of the wide-band high-resolution imaging spectropolarimetric explorer (WHISPER) currently in development for the Goode Solar Telescope.

Ilaria Ermolli, Roberto Cirami, Fabrizio Giorgi, Mariarita Murabito, Teodora Mihailescu, Igor Coretti, Veronica Baldini, Paolo Di Marcantonio, Giovanna Jerse, Antonio Sulich, Giorgio Calderone, Valentina Alberti, Sara Bertocco, Luca Oggioni, Matteo Aliverti, Maurizio Oliviero, Fabiana Ferrente, Lidia Contarino, Paolo Romano, Salvatore Luigi Guglielmino, Giorgio Viavattene, Mauro Centrone, Giorgio Frazzoni, Fernando Pedichini, Roberto Piazzesi, Dario Del Moro, Luca Giovannelli, Bernard Gelly, Richard Douet, Etienne Pariat

The IBIS 2.0 project upgrades the Interferometric BIdimensional Spectrometer (IBIS, Cavallini 2006), which operated at the Dunn Solar Telescope (DST) of the National Solar Observatory (NSO) from 2003 to 2019. IBIS 2.0 is an etalon-based imaging spectropolarimeter consisting of two FPs in a classical mounting configuration for wavelength scanning, and an LCVR-based polarimetric modulation unit for polarimetry. The upgraded instrument is being mounted at the THEMIS solar telescope in the Canary Islands. Here we present a technical overview of the instrument.

B. Lindberg, J. de la Cruz Rodríguez, J. Leenaarts, P. Sütterlin, T. Hillberg, A.G. de Wijn, L. Rouppe van der Voort, C.Pietraszewski, M. Foster, J. Storey

We discuss the requirements, concepts, simulations, implementation, and calibration of two dual Fabry-Perot (FPI)-based imaging spectropolarimeters, CHROMIS and CRISP2 (which was recently installed), at the Swedish 1-m Solar Telescope. The overall design is made robust and stable by tailoring the low-resolution etalon reflectivity to accommodate expected cavity errors from both etalons, by using a compact optical design that eliminates the need for folding mirrors, and enclosing the entire system within a single container sealed by lenses. By using a telecentric design based on lenses rather than mirrors, image degradation by the FPI system is negligible and the throughput of the system is maximised. The initial alignment is greatly simplified. The telecentric design allows the full calibration of essential system parameters to be carried out without interfering with the optical set-up or the cameras. We put forward a proposal for a similar design for the European Solar Telescope.

Because of anisoplanatism, MFBD image restoration of solar images is usually done on subfields of order 5 arcsec squared, and the results mosaicked into the larger field of view. However, the mosaicking introduces artifacts at high spatial frequences in the Fourier domain.

Different solutions to the multi-object multi-frame blind deconvolution problem using GPUs and AI are discussed.