Design, pointing control, and on-sky performance of the mid-infrared vortex coronagraph for the VLT/NEAR experiment

Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of...

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Bibliographic Details
Published in:arXiv.org 2020-12
Main Authors: A -L Maire, Huby, E, Absil, O, Zins, G, Kasper, M, Delacroix, C, Leveratto, S, Karlsson, M, Ruane, G, H -U Käufl, G Orban de Xivry, Pathak, P, Pettazzi, L, Duhoux, P, Kolb, J, Pantin, E, Eldorado Riggs, A J, Siebenmorgen, R, Mawet, D
Format: Article
Language:English
Subjects:
Adaptive optics
Coronagraphs
Experiments
Real time
Robust control
Stability
Tip tilt
Vortices
Online Access:Get full text
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Summary:Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the new Earths in the \(\alpha\) Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to \(0.015 \lambda/D\) rms over 4h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations.
ISSN:2331-8422
DOI:10.48550/arxiv.2012.08190