Compensated diffraction-limited imaging with adaptive optics at the GREGOR Solar Telescope
Kiepenheuer-Institut für Sonnenphysik Schöneckstraße 6 79104 Freiburg Germany
Natural Sciences (Astrophysics and Astrononmy)
The combination of adaptive optics with post processing of sequences of short exposures is a very successful technique to produce diffraction limited images of the solar photosphere throughout the visible spectral domain. Viable approaches are multi frame blind deconvolution and speckle imaging, and both approaches have been used with great success in the past 15 years. While blind deconvolution solves for both the undisturbed image and the optical transfer function for every frame in the sequence, speckle imaging makes assumptions about the statistics of the partially compensated wavefront and the resulting transfer functions which apply to the speckle signal. These depend on the shape of the entrance aperture and on the characteristics and performance of the adaptive optics system, and therefore need to be established separately for every telescope.
We have calculated the speckle transfer function (STF) for the GREGOR solar telescope as a function of seeing and control performance of GREGORs adaptive optics system GAOS. The calculations are based on simulations of optical propagation through an extended, turbulent atmosphere and field dependent, partial compensation by a conventional adaptive optics system. The compensation characteristics are based on actual measurements of the performance of GAOS. We present the results of the simulations and compare image reconstruction using the simulated transfer functions with reconstructions based on the previously used analytic STF models.
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