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

Abstract

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.

Published in JATIS. This version is the manuscript resubmitted before acceptance, 30 pages, 14 figures

References in corpus (5)

• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The W. M. Keck Observatory infrared vortex coronagraph and a first image of HIP79124 B
• On-sky performance of the QACITS pointing control technique with the Keck/NIRC2 vortex coronagraph
• L'-band AGPM vector vortex coronagraph's first light on LBTI/LMIRCam
• Three years of harvest with the vector vortex coronagraph in the thermal infrared

Cited by in corpus (5)

• Imaging low-mass planets within the habitable zone of α Centauri
• Experimental analysis of the achromatic performance of a vector vortex coronagraph
• Constraints on the nearby exoplanet $\epsilon$ Ind Ab from deep near/mid-infrared imaging limits
• Impact of water vapor seeing on mid-infrared high-contrast imaging at ELT scale
• Lessons learned from the NEAR experiment and prospects for the upcoming mid-IR HCI instruments