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

Milli, J. and Kasper, M. and Bourget, P. and Pannetier, C. and Mouillet, D. and Sauvage, J.-F. and Reyes, C. and Fusco, T. and Cantalloube, F. and Tristram, K. and Wahhaj, Z. and Beuzit, J.-L. and Girard, J. H. and Mawet, D. and Telle, A. and Vigan, A. and N'Diaye, M. (2018) Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results. In: Adaptive Optics Systems VI. Proceedings of SPIE. No.10703. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 107032A. ISBN 9781510619593. http://resolver.caltech.edu/CaltechAUTHORS:20180712-135345877

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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.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
https://doi.org/10.1117/12.2311499DOIArticle
ORCID:
AuthorORCID
Wahhaj, Z.0000-0001-8269-324X
Mawet, D.0000-0002-8895-4735
Vigan, A.0000-0002-5902-7828
Additional Information:© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). J.M. thanks ESO staff and technical operators at the Paranal Observatory, especially the System & Optics team for their work to apply the low-emissivity coating on the telescope spiders, and the Software team to allow to use an early release of the ESO Data Lab24 for the statistical analysis presented in this paper. He thanks W. Brandner for providing him VLTI data during a night with low wind, to evaluate the symmetry of the PSF on all 4 UTs. He thanks V. Bailey, B. Macintosh, G. Perez, M. Boccas, P. Wizinowich, J. Males, L. Close, J. Lozi and S. Vievard for providing information on the LWE and spiders properties on Gemini South, Magellan, Keck and Subaru telescopes respectively. He thanks P. Figueira for interesting discussion on statistical estimators of the LWE occurence rate. Last but not least, he thanks J. Smoker for his careful english language editing. This research has made use of the following python packages: matplotlib, pandas, scipy and astropy.
Subject Keywords:Low Wind Effect, SPHERE, Radiative Cooling, Spiders, Island Effect
Record Number:CaltechAUTHORS:20180712-135345877
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180712-135345877
Official Citation: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, "Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results", Proc. SPIE 10703, Adaptive Optics Systems VI, 107032A (10 July 2018); doi: 10.1117/12.2311499; https://doi.org/10.1117/12.2311499
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87811
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:13 Jul 2018 18:16
Last Modified:13 Jul 2018 18:16

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