Astronomy with High Contrast Imaging II
C. Aime and R. Soummer (eds)
EAS Publications Series, 12 (2004) 89-101
DOI: 10.1051/eas:2004025
The effect of a coronagraph on the statistics of Adaptive Optics Pinned Speckles
C. Aime1 and R. Soummer2
1
UMR 6525 LUAN, University of Nice Sophia-Antipolis,
06108 Nice Cedex 2, France
2
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD21218, USA
Abstract
In this communication we study the statistics of Adaptive Optics remnant speckles, and we discuss how a coronagraph can defeat
the noise associated with these speckles. At high Strehl Ratio regimes, residual speckles are pinned on the diffraction rings
of the airy pattern. It can be shown that these speckles are due to small defaults of the wavefront, amplified by the coherent
part of the wave and that the statistics of their intensity can be described by a modified Rice distribution. At low flux
levels, a Poisson-Mandel transformation provides an analytical expression of the Probablility Density Function. We show the
results of a numerical simulation and compare the results to the theoretical model. Simple analytical expressions can be derived
for the variance of the noise.
We discuss the efficiency of a coronagraph in terms of Signal to Noise Ratio, based on the analysis of the noise contributions
which can be reduced by a coronagraph.
© EAS, EDP Sciences 2004
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