On-sky compensation of non-common path aberrations with the ZELDA wavefront sensor in VLT/SPHERE

A. Vigan; M. N'Diaye; K. Dohlen; J. Milli; Z. Wahhaj; J.-F. Sauvage; J.-L. Beuzit; R. Pourcelot; D. Mouillet; G. Zins

doi:10.1117/12.2313656

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12 July 2018 On-sky compensation of non-common path aberrations with the ZELDA wavefront sensor in VLT/SPHERE

A. Vigan, M. N'Diaye, K. Dohlen, J. Milli, Z. Wahhaj, J.-F. Sauvage, J.-L. Beuzit, R. Pourcelot, D. Mouillet, G. Zins

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Proceedings Volume 10703, Adaptive Optics Systems VI; 107035O (2018) https://doi.org/10.1117/12.2313656
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

Abstract

Circumstellar environments are now routinely observed by dedicated high-contrast imagers on large, ground-based observatories. These facilities combine extreme adaptive optics and coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, non-common path aberrations (NCPA) 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 (<0.300) from their host star. In 2013 we proposed ZELDA, a Zernike wavefront sensor to measure these residual quasi-static phase aberrations and a prototype was installed in SPHERE, the exoplanet imager for the VLT. In 2016, we demonstrated the ability of our sensor to provide a nanometric calibration and compensation for these aberrations on an internal source in the instrument, resulting in a contrast gain of 10 at 0.200 in coronagraphic images. However, initial on-sky tests in 2017 did not show a tangible gain in contrast when calibrating the NCPA internally and then applying the correction on sky. In this communication, we present recent on-sky measurements to demonstrate the potential of our sensor for the NCPA compensation during observations and quantify the contrast gain in coronagraphic data. In addition, we evaluate the temporal evolution of the NCPA based on the analysis of ZELDA image sequences over hours and days.

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A. Vigan, M. N'Diaye, K. Dohlen, J. Milli, Z. Wahhaj, J.-F. Sauvage, J.-L. Beuzit, R. Pourcelot, D. Mouillet, and G. Zins "On-sky compensation of non-common path aberrations with the ZELDA wavefront sensor in VLT/SPHERE", Proc. SPIE 10703, Adaptive Optics Systems VI, 107035O (12 July 2018); https://doi.org/10.1117/12.2313656

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