Optimization of the observations of the high angular resolution techniques (adaptive optics and interferometry)

Atmospheric turbulence reduces severely the angular resolution of ground based telescopes and degrades the performances of High Angular Resolution techniques (Interferometry and Adaptive Optics). These observing methods require a better understanding of the behavior of the perturbed wavefronts, more exactly a better knowledge of the atmospheric turbulence model and the associate parameters. Indeed, the performance of an Adaptive Optics system (AO) depends upon the seeing conditions (seeing, outer scale, isoplanatic angle and wavefront coherence time). For interferometric observations, atmospheric turbulence introduces random phase variations above each telescope. The resulting variable optical path difference between the interferometer arms produces fringe displacements across the detector, which results in a blurring of the fringe pattern and therefore a degradation of the fringe contrast observed. We describe, here, a seeing measurement of the spatial coherence outer scale and the wavefront coherence diameter from interferometric data. First results obtained with the GI2T ("Grand Interferometre a 2 Telescopes") interferometer at the Calern Observatory are presented and compared to those measured directly and simultaneously with the GSM ("Generalized Seeing Monitor").

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