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Proceedings Paper

The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2
Author(s): Elsa Huby; Olivier Absil; Dimitri Mawet; Pierre Baudoz; Bruno Femenìa Castellà; Michael Bottom; Henry Ngo; Eugene Serabyn
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Paper Abstract

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.

Paper Details

Date Published: 26 July 2016
PDF: 10 pages
Proc. SPIE 9909, Adaptive Optics Systems V, 990920 (26 July 2016); doi: 10.1117/12.2233274
Show Author Affiliations
Elsa Huby, Univ. de Liège (Belgium)
Olivier Absil, Univ. de Liège (Belgium)
Dimitri Mawet, California Institute of Technology (United States)
Pierre Baudoz, LESIA, Observatoire de Paris, CNRS, UPMC, Univ. Paris-Diderot (France)
Bruno Femenìa Castellà, W. M. Keck Observatory (United States)
Michael Bottom, California Institute of Technology (United States)
Henry Ngo, California Institute of Technology (United States)
Eugene Serabyn, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 9909:
Adaptive Optics Systems V
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)

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