Active minimization of non-common path aberrations in long-exposure imaging of exoplanetary systems

Abstract

Context. Spectroscopy of exoplanets is very challenging because of the high star-planet contrast. A technical difficulty in the design of imaging instruments is the noncommon path aberrations (NCPAs) between the adaptive optics (AO) sensing and the science camera, which induce planet-resembling stellar speckles in the coronagraphic science images. In an observing sequence of several long exposures, quickly evolving NCPAs average out and leave behind an AO halo that adds photon noise to the planet detection. Static NCPA can be calibrated a posteriori using differential imaging techniques. However, NCPAs that evolve during the observing sequence do not average out and cannot be calibrated a posteriori. These quasi-static NCPAs are one of the main limitations of the current direct imaging instruments such as SPHERE, GPI, and SCExAO. Aims. Our aim is to actively minimize the quasi-static speckles induced in long-exposure images. To do so, we need to measure the quasi-static speckle field above the AO halo. Methods. The self-coherent camera (SCC) is a proven technique which measures the speckle complex field in the coronagraphic science images. It is routinely used on the THD2 bench to reach contrast levels of <10^{-8} in the range 5-12 λ/D in space-related conditions. To test the SCC in ground conditions on THD2, we optically simulated the residual aberrations measured behind the SPHERE/VLT AO system under good observing conditions. Results. We demonstrate in the laboratory that the SCC can minimize the quasi-static speckle intensity in the science images down to a limitation set by the AO halo residuals. The SCC reaches 1σ raw contrast levels below 10^{-6} in the region 5-12 λ/D at 783.25 nm in our experiments.

arXiv comment10 pages, 11 figures, accepted for publication to A&A

References in corpus (22)

• Angular Differential Imaging: a Powerful High-Contrast Imaging Technique
• The Gemini Planet Imager: First Light
• SPHERE: the exoplanet imager for the Very Large Telescope
• The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
• Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
• Limits of Adaptive Optics for high contrast imaging
• High-contrast Imaging from Space: Speckle Nulling in a Low Aberration Regime
• High Dynamic Range Imaging Using a Deformable Mirror for Space Coronography
• Fundamental limitations on Earth-like planet detection with Extremely Large Telescopes
• On-sky speckle nulling demonstration at small angular separation with SCExAO
• Coronagraphic Survey for Companions of Stars within 8 pc
• Self-coherent camera as a focal plane wavefront sensor: simulations
• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. III. On-sky validation in VLT/SPHERE
• The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments
• Estimation and correction of wavefront aberrations using the self-coherent camera: laboratory results
• High-contrast imaging in polychromatic light with the self-coherent camera
• Speckle temporal stability in XAO coronagraphic images II. Refine model for quasi-static speckle temporal evolution for VLT/SPHERE
• Speckle suppression and companion detection using coherent differential imaging
• Speckle Temporal Stability in eXtreme Adaptive Optics Coronagraphic Images
• Near-IR coronagraphic imaging of the companion to HR 7672
• Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD-testbed
• Speckle lifetime in XAO coronagraphic images: temporal evolution of SPHERE coronagraphic images

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• Increasing the raw contrast of VLT/SPHERE with the dark-hole technique. II. On-sky wavefront correction and coherent differential imaging
• The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing
• First on-sky demonstration of spatial Linear Dark Field Control with the vector-Apodizing Phase Plate at Subaru/SCExAO
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