Simulation algorithm to model the visible tunable filter for the Daniel K. Inouye Solar Telescope

Journal of astronomical telescopes, instruments, and systems : JATIS 3 (2017), Nr. 0

Étude de la dynamique des couches sub-photosphériques par l'héliosismologie locale

This thesis is a contribution work to the study of the dynamics of sub-surface layers of the Sun using the actual long-term high resolution helioseismic data. The inner solar structure has also been studied in the light of the new estimates of solar chemical heavy element abundances which are currently one of the most debated issues in the field of solar interior modelling. Findings in this topic concern the low degree acoustic modes that turned out to be sensitive to the change ion the solar abundances. Notably, the new estimates of solar abundances lead to conflicting calculations of the characteristics of these modes with the observation. Ring diagram analysis of solar Doppler images has been used to infer the sub-photospheric horizontal velocity flows. The sensitivity of this technique has been studied regarding the mapping of solar images and the appropriate geometrical projection has been inferred. Moreover, the impact of solar modelling on the inversion procedure leading to the internal flows has been studied. Seven years of continuous GONG data corresponding to the declining phase of solar cycle 23 have been analyzed using the ring diagram method to infer long-term variations of horizontal flow fields (meridional and zonal flows) in latitude, longitude, and depth. Many interesting behaviours of the flows have been found such as the acceleration of the meridional flow and the dominance of the dynamics of the southern hemisphere relative to the northern one. The radial gradient of solar rotation has also been studied in detail showing an unusual behaviour of this gradient that appeared at the beginning of the long minimum period of solar cycle 23.Cette thèse est une contribution à l étude de la dynamique des couches subphotosphériques à travers l analyse des données héliosismiques à haute résolution, actuellement disponible pour plusieurs années. La structure des couches profondes a aussi été étudiée dans le contexte des nouvelles abondances solaires qui représentent, de nos jours, l un des sujets les plus débattus en physique solaire. Dans ce contexte, la sensibilité des modes acoustiques solaires de bas degrés au changement d abondances a été montrée. Notamment, les nouvelles abondances ont induit d importantes incompatibilités entre le calcul des caractéristiques de ces modes et l observation. Ma méthode dite des diagrammes en anneaux des images Doppler a été utilisée pour obtenir les vitesses horizontales des couches sub-photosphériques. La sensibilité de la technique à la cartographie des images solaires a été étudiée et la projection géométrique la mieux appropriée a été déduite. De plus, l impact de la modélisation de la structure sur la procédure d inversion menant aux estimations des vitesses a été étudié. Sept années continues de données GONG, correspondant à la phase descendante du cycle solaire 23, ont été analysées ar la méthode des diagrammes en anneaux. La variation à long terme de la circulation méridienne et du flux zonal en latitude, longitude et rayon a été déduite. D importants comportements des vitesses ont été observés, notamment, l accélération du flux méridien et la prédominance des vitesses de l hémisphère sud sur celles de l hémisphère nord. Le gradient radial de la rotation a aussi été étudié en détail, montrant un comportement inhabituel au début de la longue époque du minimum solaire du cycle 23.NICE-BU Sciences (060882101) / SudocSudocFranceF

Characterization of optical turbulence at the GREGOR solar telescope: Temporal and local behavior and its influence on the solar observations

Local atmospheric turbulence at the telescope level is regarded as a major reason for affecting the performance of the adaptive optics systems using wavelengths in the visible and infrared for solar observations. During the day the air masses around the telescope dome are influenced by flow distortions. Additionally heating of the infrastructure close to telescope causes thermal turbulence. Thereby optical turbulence is produced and leads to quality changes in the local seeing throughout the day. Image degradation will be yielded affecting the performance of adaptive optical systems. The spatial resolution of the solar observations will be reduced. For this study measurements of the optical turbulence, represented by the structure function parameter of the refractive index Cn2 were performed on several locations at the GREGOR telescope at the Teide observatory at Tenerife at the Canary Islands / Spain. Since September 2012 measurements of Cn2 were carried out between the towers of the Vacuum Tower Telescope (VTT) and of GREGOR with a laser-scintillometer. The horizontal distance of the measurement path was about 75 m. Additional from May 2015 up to March 2016 the optical turbulence was determined at three additional locations close to the solar telescope GREGOR. The optical turbulence is derived from sonic anemometer measurements. Time series of the sonic temperature are analyzed and compared to the direct measurements of the laser scintillometer. Meteorological conditions are investigated, especially the influence of the wind direction. Turbulence of upper atmospheric layers is not regarded. The measured local turbulence is compared to the system performance of the GREGOR telescopes. It appears that the mountain ridge effects on turbulence are more relevant than any local causes of seeing close to the telescope. Results of these analyses and comparison of nearly one year of measurements are presented and discussed

Simulation of adaptive optics for the Vacuum Tower Telescope

A simulation model of the adaptive optics of the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerifes presented. The model uses modules from the integrated model of the Euro50 extremely large telescope, and includes submodels of a Shack-Hartmann wavefront sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier low-pass filters, a reconstructor and a controller. We investigate the impact on the closed loop bandwidth of changes in controller configuration and certain system parameters, such as low pass filter bandwidth and camera integration and readout time. Control strategies were tested on simple models before implementation on the full VTT model. Using the models, different control strategies are compared

widens the field for observations of the Sun with multi-conjugate adaptive optics

The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasi-simultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53′′ field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the images

Clear widens the field for observations of the Sun with multi-conjugate adaptive optics

The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasi-simultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53′′ field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the image