EAS Publications Series
Volume 12, 2004Astronomy with High Contrast Imaging II
|Page(s)||89 - 101|
|Published online||11 October 2004|
C. Aime and R. Soummer (eds)
EAS Publications Series, 12 (2004) 89-101
The effect of a coronagraph on the statistics of Adaptive Optics Pinned Speckles
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
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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