13 September 2012 MCAO: Wavefront sensing only as a tool for high precision photometry?
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In MCAO the correction of the wavefront for an extended Field of View is obtained at the expense of a stretching of the actual instantaneous meta-pupils over the high altitude layers, just to compensate their average curvature. While this effect does average out in long term exposures and is of secondary interest in compensated imaging, it gives the input for the idea of using MCAO-like information, collectable over a certain Field of View, to assess in a time resolved mode (not necessarily in real time) the actual geometrical light throughput in a given direction. In principle this would allow, with proper time tagging, to achieve high precision photometry, as part of the scintillation could be measured on line during the observation. Simple averaging of neighbor stars to flat field starlight, for example, represents the equivalent of this concept for the ground-layer correction only. It can be seen that, once a direction is defined, it is relevant only the derivative of the wavefront around or in the proximity of that edges, but the range at which this happen is a crucial parameter. However, the strong interest in high precision measurements of exoplanetary transits or asteroseismology could make this approach not as lunatic as it could sound. view
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V. Viotto, R. Ragazzoni, M. Bergomi, A. Brunelli, M. Dima, J. Farinato, D. Magrin, L. Marafatto, V. Nascimbeni, G. Piotto, "MCAO: Wavefront sensing only as a tool for high precision photometry?", Proc. SPIE 8447, Adaptive Optics Systems III, 84476X (13 September 2012); doi: 10.1117/12.926370; https://doi.org/10.1117/12.926370

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