A Machine Learning Approach to Correcting Atmospheric Seeing in Solar Flare Observations

Current post-processing techniques for the correction of atmospheric seeing in solar observations – such as Speckle interferometry and Phase Diversity methods – have limitations when it comes to their reconstructive capabilities of solar flare observations. This, combined with the sporadic nature of flares meaning observers cannot wait until seeing conditions are optimal before taking measurements, means that many ground-based solar flare observations are marred with bad seeing. To combat this, we propose a method for dedicated flare seeing correction based on training a deep neural network to learn to correct artificial seeing from flare observations taken during good seeing conditions. This model uses transfer learning, a novel technique in solar physics, to help learn these corrections. Transfer learning is when another network already trained on similar data is used to influence the learning of the new network. Once trained, the model has been applied to two flare datasets: one from AR12157 on 2014/09/06 and one from AR12673 on 2017/09/06. The results show good corrections to images with bad seeing with a relative error assigned to the estimate based on the performance of the model. Further discussion takes place of improvements to the robustness of the error on these estimates.

NAOMI: the adaptive optics system of the Auxiliary Telescopes of the VLTI

Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. Aims. Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the instruments, and enable robust fringe tracking even in degraded conditions. Methods. We deployed a new adaptive optics module for interferometry (NAOMI) on the Auxiliary Telescopes. Results. We present its design, performance, and effect on the observations that are carried out with the interferometric instruments.

Adaptive Optics for Extremely Large Telescopes

Adaptive Optics (AO) has become a key technology for the largest ground-based telescopes currently under, or close to beginning of, construction. AO is an indispensable component and has basically only one task, that is to operate the telescope at its maximum angular resolution, without optical degradations resulting from atmospheric seeing. Based on three decades of experience using AO usually as an add-on component, all extremely large telescopes and their instrumentation are designed for diffraction limited observations from the very beginning. This paper illuminates various approaches of the ELT, the Giant Magellan Telescope (GMT), and the Thirty-Meter Telescope (TMT), to fully integrate AO in their designs. The paper concludes with a brief look into the requirements that high-contrast imaging poses on AO.

SOWAT: High-resolution imaging with only partial AO correction

Observations of dense stellar systems such as globular clusters (GCs) are limited in resolution by the optical aberrations induced by atmospheric turbulence (atmospheric seeing). At the example of holographic speckle imaging, we now study, to which degree image reconstruction algorithms are able to remove residual aberrations from a partial adaptive optics (AO) correction, such as delivered from ground-layer AO (GLAO) systems. Simultaneously, we study, how such algorithms benefit from being applied to pre-corrected instead of natural point-spread functions (PSFs). We find that using partial AO corrections already lowers the demands on the holography reference star by ∼3 mag, what makes more fields accessible for this technique, and also that the discrete integration times may be chosen about 2–3× longer, since the effective wavefront evolution is slowed down by removing the perturbation power.

The Four-Laser Guide Star Facility: Design considerations and system implementation

Ground-based optical telescopes, in particular large ones, require adaptive optics to overcome the atmospheric seeing limit due to turbulence. Correcting the distorted wavefront necessitates bright stars in the field of view. The sky coverage can be greatly increased by using artificial sodium laser guide stars in addition to natural guide stars. We describe the underlying physics and technical considerations relevant to such systems before discussing the design of the four-laser guide star facility (4LGSF) which is currently under development for the ESO Very Large Telescope (VLT) on Cerro Paranal, Chile. The focus is upon the justification of the requirements and their technical solution.

LOW FREQUENCY SEEING AND SOLAR DIAMETER MEASUREMENTS

The action of the atmospheric seeing is blurring, image stretching and image motion. This happens even to the image of the Sun which is more than half degree wide. Low frequency seeing components affect the solar diameter values measured either through the drift-scan or the heliometer methods. We present evidences of image motion and stretching down to 0.001 Hz.