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Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results
Author(s): J. Milli; M. Kasper; P. Bourget; C. Pannetier; D. Mouillet; J.-F. Sauvage; C. Reyes; T. Fusco; F. Cantalloube; K. Tristam; Z. Wahhaj; J.-L. Beuzit; J. H. Girard; D. Mawet; A. Telle; A. Vigan; M. N'Diaye
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Paper Abstract

The low wind effect is a phenomenon disturbing the phase of the wavefront in the pupil of a large telescope obstructed by spiders, in the absence of wind. It can be explained by the radiative cooling of the spiders, creating air temperature inhomogeneities across the pupil. Because it is unseen by traditional adaptive optics (AO) systems, thus uncorrected, it significantly degrades the quality of AO-corrected images. We provide a statistical analysis of the strength of this effect as seen by VLT/SPHERE after 4 years of operations. We analyse its dependence upon the wind and temperature conditions. We describe the mitigation strategy implemented in 2017: a specific coating with low thermal emissivity in the mid-infrared was applied on the spiders of Unit Telescope 3. We quantify the improvement in terms of image quality, contrast and wave front error using both focal plane images and measured phase maps.

Paper Details

Date Published: 10 July 2018
PDF: 20 pages
Proc. SPIE 10703, Adaptive Optics Systems VI, 107032A (10 July 2018); doi: 10.1117/12.2311499
Show Author Affiliations
J. Milli, European Southern Observatory (Chile)
M. Kasper, European Southern Observatory (Germany)
P. Bourget, European Southern Observatory (Chile)
C. Pannetier, European Southern Observatory (Chile)
D. Mouillet, Univ. Grenoble Alpes (France)
Institut de Planétologie et d’Astrophysique de Grenoble (France)
J.-F. Sauvage, Aix-Marseille Univ., CNRS, Lab. d'Astrophysique de Marseille (France)
ONERA (France)
C. Reyes, European Southern Observatory (Chile)
T. Fusco, Aix-Marseille Univ., CNRS, Lab. d'Astrophysique de Marseille (France)
ONERA (France)
F. Cantalloube, Max Planck Institute for Astronomy (Germany)
K. Tristam, European Southern Observatory (Chile)
Z. Wahhaj, European Southern Observatory (Chile)
J.-L. Beuzit, European Southern Observatory (Germany)
J. H. Girard, Space Telescope Science Institute (United States)
D. Mawet, California Institute of Technology (United States)
Jet Propulsion Lab. (United States)
A. Telle, ACM Coatings GmbH (Germany)
A. Vigan, Aix-Marseille Univ., CNRS, Lab. d'Astrophysique de Marseille (France)
M. N'Diaye, Univ. Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Lab. Lagrange (France)

Published in SPIE Proceedings Vol. 10703:
Adaptive Optics Systems VI
Laird M. Close; Laura Schreiber; Dirk Schmidt, Editor(s)

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