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

Milli, J.; Kasper, Markus; Bourget, P.; Pannetier, Cyril; Mouillet, D.; Sauvage, Jean-François; Reyes, Claudia; Fusco, Thierry; Cantalloube, F.; Tristam, Konrad; Wahhaj, Z.; Beuzit, Jean-Luc; Girard, J.; Mawet, Dimitri; Telle, Alexander; Vigan, A.; N’Diaye, Mamadou

doi:10.1117/12.2311499

Cited by 28 publications

(29 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The presence of spiders has recently been shown to be at the origin of the "low wind effect," which creates additional aberrations at low spatial frequencies that are not well detected by standard Shack-Hartmann PyWFSs. 53 Even worse, the discontinuity of the pupil can lead to an artificial buildup of piston error between petals in closed-loop AO operations. Fortunately, the near-infrared PyWFS used in METIS is more robust to this petal piston mode, and specific reconstruction and control strategies are being implemented to mitigate this effect.…”

Section: Petal Pistonmentioning

confidence: 99%

METIS high-contrast imaging: design and expected performance

Carlomagno

Delacroix

Absil

et al. 2020

J. Astron. Telesc. Instrum. Syst.

View full text Add to dashboard Cite

With the advent of 30-to 40-m class ground-based telescopes in the mid-2020s, direct imaging of exoplanets is bound to take a new major leap. Among the approved projects, the Mid-infrared Extremely Large Telescope (ELT) Imager and Spectrograph (METIS) instrument for the ELT holds a prominent spot; by observing in the mid-infrared regime, it will be perfectly suited to study a variety of exoplanets and protoplanetary disks around nearby stars. Equipped with two of the most advanced coronagraphs, the vortex coronagraph and the apodizing phase plate, METIS will provide high-contrast imaging (HCI) in L-, Mand N-bands, and a combination of high-resolution spectroscopy and HCI in Land M-bands. We present the expected HCI performance of the METIS instrument, considering realistic adaptive optics residuals, and investigate the effect of the main instrumental errors. The most important sources of degradation are identified and realistic sensitivity limits in terms of planet/star contrast are derived. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

show abstract

Section: Petal Pistonmentioning

confidence: 99%

METIS high-contrast imaging: design and expected performance

Carlomagno

Delacroix

Absil

et al. 2020

J. Astron. Telesc. Instrum. Syst.

View full text Add to dashboard Cite

show abstract

“…LWE was only recently successfully diagnosed on VLT/SPHERE [7] and a new mitigation strategy was recently proposed and implementer at the end of 2017, when a coating with low thermal (in the mid-infrared) emissivity was fixed to the spiders. This has been shown to dramatically reduce the LWE by a factor around 5 as a first approximation [11]. However this reduction needs to be quantified in the case of ELT instruments and in particular for HARMONI.…”

Section: Low Wind Effectmentioning

confidence: 97%

“…Low Wind Effect (LWE) aberrations are created by air temperature gradients at the level of the telescope spiders. The physical origin of the LWE is well explained [7,11] by the radiative cooling of the telescope spiders, creating nonuniform air temperatures across the telescope pupil. The wavefront steps across the pupil are extremely sharp, defined by the spider arm.…”

Section: Low Wind Effectmentioning

confidence: 99%

Analysis and mitigation of pupil discontinuities on adaptive optics performance

Schwartz

Sauvage

Correia

et al. 2018

Adaptive Optics Systems VI

Self Cite

View full text Add to dashboard Cite

As already noticed in other telescopes, the presence of large telescope spiders and of a segmented deformable mirror in an Adaptive Optics system leads to pupil fragmentation and may create phase discontinuities. On the ELT telescope, a typical effect is the differential piston, where all disconnected areas of the pupil create their own piston, unseen locally but drastically degrading the final image quality. The poor sensitivity of the Pyramid WFS to differential piston will lead to these modes been badly seen and therefore badly controlled by the adaptive optics (AO) loop. In close loop operation, differential pistons between segments will start to appear and settle around integer values of the average sensing wavelength. These additional differential pistons are artificially injected by the adaptive optics control loop but do not have any real physical origin, contrary to the Low Wind Effect. In an attempt to reduce the impact of unwanted differential pistons that are injected by the AO loop, we propose a novel approach based on the pair-wise coupling of the actuators sitting on the edges of the deformable mirror segments. In this paper, we present the correction principle, its performance in nominal seeing condition, and its robustness relative to changing seeing conditions, wind speed and natural guide star magnitude. We show that the edge actuator coupling is a simple and robust solution and that the additional quadratic error relative to the reference case (i.e. no spiders) is of only 40 nm RMS, well within the requirements for HARMONI.

show abstract

“…Since it would go beyond the scope of this review, here are just two current examples. The SPHERE XAO system installed at the Paranal observatory discovered a so called low wind e®ect Milli et al (2018) (sometimes also named island e®ect), which basically distorts the wavefronts in the pupil of large telescopes obstructed by Fig. 3.…”

Section: Wide-¯eld and Extreme Aomentioning

confidence: 99%

Adaptive Optics for Extremely Large Telescopes

Hippler

2019

J. Astron. Instrum.

View full text Add to dashboard Cite

Adaptive Optics (AO) has become a key technology for the largest ground-based telescopes currently under, or close to beginning of, construction. AO is an indispensable component and has basically only one task, that is to operate the telescope at its maximum angular resolution, without optical degradations resulting from atmospheric seeing. Based on three decades of experience using AO usually as an add-on component, all extremely large telescopes and their instrumentation are designed for di®raction limited observations from the very beginning. This paper illuminates various approaches of the ELT, the Giant Magellan Telescope (GMT), and the Thirty-Meter Telescope (TMT), to fully integrate AO in their designs. The paper concludes with a brief look into the requirements that high-contrast imaging poses on AO.

show abstract

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

Cited by 28 publications

References 18 publications

METIS high-contrast imaging: design and expected performance

METIS high-contrast imaging: design and expected performance

Analysis and mitigation of pupil discontinuities on adaptive optics performance

Adaptive Optics for Extremely Large Telescopes

Contact Info

Product

Resources

About