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Published July 10, 2018 | Version Published
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Low wind effect on VLT/SPHERE: impact, mitigation strategy, and results

Creators

  • 1. ROR icon European Southern Observatory
  • 2. ROR icon Grenoble Alpes University
  • 3. ROR icon Institut de Planétologie et d'Astrophysique de Grenoble
  • 4. ROR icon Laboratoire d'Astrophysique de Marseille
  • 5. ROR icon Office National d'Études et de Recherches Aérospatiales
  • 6. ROR icon Max Planck Institute for Astronomy
  • 7. ROR icon Space Telescope Science Institute
  • 8. ROR icon California Institute of Technology
  • 9. ROR icon Jet Propulsion Lab
  • 10. ROR icon Observatoire de la Côte d'Azur

Contributors

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.

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.

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Identifiers

Eprint ID
87811
Resolver ID
CaltechAUTHORS:20180712-135345877

Dates

Created
2018-07-13
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Updated
2021-11-15
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Caltech Custom Metadata

Caltech groups
Astronomy Department
Series Name
Proceedings of SPIE
Series Volume or Issue Number
10703