An analytic expression for coronagraphic imaging through turbulence. Application to on-sky coronagraphic phase diversity

Abstract

The ultimate performance of coronagraphic high contrast exoplanet imaging systems such as SPHERE or GPI is limited by quasi-static aberrations. These aberrations produce speckles that can be mistaken for planets in the image. In order to design instruments, correct quasi-static aberrations or analyse data, the expression of the point spread function of a coronagraphic instrument in the presence of residual turbulence is most useful. Here we derive an analytic expression for this point spread function that is an extension to coronagraphic imaging of Roddier's expression for imaging through turbulence. We give a physical interpretation of its structure, we validate it by numerical simulations and we show that it is computationally efficient. Finally, we incorporate this imaging model into a coronagraphic phase diversity method (COFFEE) and validate by simulations that it allows wave-front reconstruction in the presence of residual turbulence. The preliminary results, which give a sub-nanometric precision in the case of a SPHERE-like system, strongly suggest that quasi-static aberrations could be calibrated during observations by this method.

This is a pre-copyedited, author-produced PDF of an article accepted for publication in the monthly notices of the royal astronomical society following peer review, MNRAS 2017 slx009

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• Millisecond Exoplanet Imaging, I: Method and Simulation Results
• Coronagraphic phase diversity through residual turbulence: performance study and experimental validation
• Analytical modelling of adaptive optics systems: Role of the influence function
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• The Mysterious Lives Of Speckles. I. Residual atmospheric speckle lifetimes in ground-based coronagraphs
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