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Gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments on large, ground-based observatories. These facilities combine extreme adaptive optics and coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, residual quasi-static phase aberrations in these coronagraphic systems represent a critical limitation for the detection of giant planets with a contrast lower than a few 10−6 at very small separations (<0.3′′) from their host star. In 2013 we proposed ZELDA, a Zernike wavefront sensor to measure these phase aberrations at a nanometric level. Relying on a prototype installed in VLT/SPHERE in 2014, we performed multiple tests in December 2015 and demonstrated the capability of our concept to accurately measure well-known aberrations on internal source. We also showed a contrast improvement by a factor of 10 at 0.2′′ for this instrument by calibrating its residual aberrations with our device. After a brief review of this experimental validation, we present preliminary on-sky results on SPHERE obtained in March 2017. This new data set relies on ZELDA estimate of quasi-static aberrations on the internal source. We finally discuss perspectives for future ELT instrumentation with ZELDA.

ZELDA, a Zernike sensor for accurate calibration of aberrations in coronagraphic instruments: validation in VLT/SPHERE and preliminary on-sky results