Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results

Milli, J.; Kasper, M.; Bourget, P.; Pannetier, C.; Mouillet, D.; Sauvage, J. -F.; Reyes, C.; Fusco, T.; Cantalloube, F.; Tristam, K.; Wahhaj, Z.; Beuzit, J. -L.; Girard, J. H.; Mawet, D.; Telle, A.; Vigan, A.; N'Diaye, M.

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Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results

MPS-Authors

Milli, J.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Kasper, M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Bourget, P.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Pannetier, C.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Mouillet, D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Sauvage, J. -F.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Reyes, C.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Fusco, T.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Cantalloube, F.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Tristam, K.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Wahhaj, Z.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Beuzit, J. -L.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Girard, J. H.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Mawet, D.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Telle, A.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Vigan, A.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

N'Diaye, M.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

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https://ui.adsabs.harvard.edu/abs/2018SPIE10703E..2AM
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Citation

Milli, J., Kasper, M., Bourget, P., Pannetier, C., Mouillet, D., Sauvage, J.-.-F., et al. (2018). Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results.

Cite as: https://hdl.handle.net/21.11116/0000-0005-CC24-D

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.