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The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2

Huby, Elsa and Absil, Olivier and Mawet, Dimitri and Baudoz, Pierre and Femenìa, Castellà and Bottom, Michael and Ngo, Henry and Serabyn, Eugene (2016) The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2. In: Adaptive Optics Systems V. Proceedings of SPIE. No.9909. Society of Photo-Optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 990920. ISBN 978-1-5106-0198-7.

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Small inner working angle coronagraphs are essential to benefit from the full potential of large and future extremely large ground-based telescopes, especially in the context of the detection and characterization of exoplanets. Among existing solutions, the vortex coronagraph stands as one of the most effective and promising solutions. However, for focal-plane coronagraph, a small inner working angle comes necessarily at the cost of a high sensitivity to pointing errors. This is the reason why a pointing control system is imperative to stabilize the star on the vortex center against pointing drifts due to mechanical flexures, that generally occur during observation due for instance to temperature and/or gravity variations. We have therefore developed a technique called QACITS1 (Quadrant Analysis of Coronagraphic Images for Tip-tilt Sensing), which is based on the analysis of the coronagraphic image shape to infer the amount of pointing error. It has been shown that the flux gradient in the image is directly related to the amount of tip-tilt affecting the beam. The main advantage of this technique is that it does not require any additional setup and can thus be easily implemented on all current facilities equipped with a vortex phase mask. In this paper, we focus on the implementation of the QACITS sensor at Keck/NIRC2, where an L-band AGPM has been recently commissioned (June and October 2015), successfully validating the QACITS estimator in the case of a centrally obstructed pupil. The algorithm has been designed to be easily handled by any user observing in vortex mode, which is available for science in shared risk mode since 2016B.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Absil, Olivier0000-0002-4006-6237
Mawet, Dimitri0000-0002-8895-4735
Bottom, Michael0000-0003-1341-5531
Ngo, Henry0000-0001-5172-4859
Additional Information:© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).
Subject Keywords:Wavefront sensing, vector vortex coronagraph, tip-tilt sensor, pointing sensor
Series Name:Proceedings of SPIE
Issue or Number:9909
Record Number:CaltechAUTHORS:20161205-080638386
Persistent URL:
Official Citation:Elsa Huby ; Olivier Absil ; Dimitri Mawet ; Pierre Baudoz ; Bruno Femenìa Castellà ; Michael Bottom ; Henry Ngo ; Eugene Serabyn; The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2. Proc. SPIE 9909, Adaptive Optics Systems V, 990920 (July 26, 2016); doi:10.1117/12.2233274.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:72544
Deposited On:07 Dec 2016 00:18
Last Modified:11 Nov 2021 05:03

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