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Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO

N’Diaye, M. and Martinache, F. and Jovanovic, N. and Lozi, J. and Guyon, O. and Norris, B. and Ceau, A. and Mary, D. (2018) Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO. Astronomy and Astrophysics, 610 . Art. No. A18. ISSN 0004-6361. doi:10.1051/0004-6361/201731985.

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Context. Island effect (IE) aberrations are induced by differential pistons, tips, and tilts between neighboring pupil segments on ground-based telescopes, which severely limit the observations of circumstellar environments on the recently deployed exoplanet imagers (e.g., VLT/SPHERE, Gemini/GPI, Subaru/SCExAO) during the best observing conditions. Caused by air temperature gradients at the level of the telescope spiders, these aberrations were recently diagnosed with success on VLT/SPHERE, but so far no complete calibration has been performed to overcome this issue. Aims. We propose closed-loop focal plane wavefront control based on the asymmetric Fourier pupil wavefront sensor (APF-WFS) to calibrate these aberrations and improve the image quality of exoplanet high-contrast instruments in the presence of the IE. Methods. Assuming the archetypal four-quadrant aperture geometry in 8 m class telescopes, we describe these aberrations as a sum of the independent modes of piston, tip, and tilt that are distributed in each quadrant of the telescope pupil. We calibrate these modes with the APF-WFS before introducing our wavefront control for closed-loop operation. We perform numerical simulations and then experimental tests on a real system using Subaru/SCExAO to validate our control loop in the laboratory and on-sky. Results. Closed-loop operation with the APF-WFS enables the compensation for the IE in simulations and in the laboratory for the small aberration regime. Based on a calibration in the near infrared, we observe an improvement of the image quality in the visible range on the SCExAO/VAMPIRES module with a relative increase in the image Strehl ratio of 37%. Conclusions. Our first IE calibration paves the way for maximizing the science operations of the current exoplanet imagers. Such an approach and its results prove also very promising in light of the Extremely Large Telescopes (ELTs) and the presence of similar artifacts with their complex aperture geometry.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
N’Diaye, M.0000-0002-1721-3294
Martinache, F.0000-0003-1180-4138
Lozi, J.0000-0002-3047-1845
Guyon, O.0000-0002-1097-9908
Additional Information:© ESO, 2018. Received 23 September 2017 / Accepted 15 November 2017. This work is supported by the European Research Council (ERC) through the KERNEL project grant #683029 (PI: F. Martinache). M.N. would like to thank Alain Spang for very engaging conversations on the identification and diagnostic of the island effect by Couder (1949) with a Foucault knife-edge test on an 80 cm telescope at Observatoire de Haute Provence. This work was supported by the Astrobiology Center (ABC) of the National Institutes of Natural Sciences, Japan and the directors contingency fund at the Subaru Telescope. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
European Research Council (ERC)683029
National Institutes of Natural Sciences of JapanUNSPECIFIED
Subaru TelescopeUNSPECIFIED
Subject Keywords:instrumentation: high angular resolution / instrumentation: adaptive optics / techniques: high angular resolution / telescopes / methods: data analysis
Record Number:CaltechAUTHORS:20181130-105341390
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Official Citation:Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO M. N’Diaye, F. Martinache, N. Jovanovic, J. Lozi, O. Guyon, B. Norris, A. Ceau and D. Mary A&A, 610 (2018) A18 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91365
Deposited By: George Porter
Deposited On:03 Dec 2018 15:59
Last Modified:16 Nov 2021 03:40

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