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 .