On-sky performance of the QACITS pointing control technique with the Keck/NIRC2 vortex coronagraph

Abstract

A vortex coronagraph is now available for high contrast observations with the Keck/NIRC2 instrument at L band. Reaching the optimal performance of the coronagraph requires fine control of the wavefront incident on the phase mask. In particular, centering errors can lead to significant stellar light leakage that degrades the contrast performance and prevents the observation of faint planetary companions around the observed stars. It is thus critical to correct for the possible slow drift of the star image from the phase mask center, generally due to mechanical flexures induced by temperature and/or gravity field variation, or to misalignment between the optics that rotate in pupil tracking mode. A control loop based on the QACITS algorithm for the vortex coronagraph has thus been developed and deployed for the Keck/NIRC2 instrument. This algorithm executes the entire observing sequence, including the calibration steps, initial centering of the star on the vortex center and stabilisation during the acquisition of science frames. On-sky data show that the QACITS control loop stabilizes the position of the star image down to 2.4 mas rms at a frequency of about 0.02 Hz. However, the accuracy of the estimator is probably limited by a systematic error due to a misalignment of the Lyot stop with respect to the entrance pupil, estimated to be on the order of 4.5 mas. A method to reduce the amplitude of this bias down to 1 mas is proposed. The QACITS control loop has been successfully implemented and provides a robust method to center and stabilize the star image on the vortex mask. In addition, QACITS ensures a repeatable pointing quality and significantly improves the observing efficiency compared to manual operations. It is now routinely used for vortex coronagraph observations at Keck/NIRC2, providing contrast and angular resolution capabilities suited for exoplanet and disk imaging.

arXiv comment9 pages, 13 figures. Accepted for publication in A&A

References in corpus (16)

• Detection and Characterization of Exoplanets and Disks using Projections on Karhunen-Loeve Eigenimages
• The Gemini Planet Imager: First Light
• The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
• PynPoint: An Image Processing Package for Finding Exoplanets
• Phase-Induced Amplitude Apodization of Telescope Pupils for Extrasolar Terrestrial Planet Imaging
• The Vector Vortex Coronagraph: Laboratory Results and First Light at Palomar Observatory
• Low-rank plus sparse decomposition for exoplanet detection in direct-imaging ADI sequences. The LLSG algorithm
• The W. M. Keck Observatory infrared vortex coronagraph and a first image of HIP79124 B
• Lyot-based Low Order Wavefront Sensor for Phase-mask Coronagraphs: Principle, Simulations and Laboratory Experiments
• Post-coronagraphic tip-tilt sensing for vortex phase masks: the QACITS technique
• Coronagraphic Low Order Wavefront Sensor: Principle and Application to a Phase-Induced Amplitude Coronagraph
• Characterization of the inner disk around HD 141569 A from Keck/NIRC2 L-band vortex coronagraphy
• Speckle suppression and companion detection using coherent differential imaging
• Optimizing the subwavelength grating of L-band Annular Groove Phase Masks for high coronagraphic performance
• On-sky demonstration of low-order wavefront sensing and control with focal plane phase mask coronagraphs
• The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2

Cited by in corpus (23)

• Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758
• Keck/NIRC2 $L$'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
• Reference star differential imaging of close-in companions and circumstellar disks with the NIRC2 vortex coronagraph at W.M. Keck Observatory
• Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged Inside the Debris Disk of the Young Star AF Lep
• Deep exploration of $\epsilon$ Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet
• Characterizing the performance of the NIRC2 vortex coronagraph at W.M. Keck Observatory
• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. III. On-sky validation in VLT/SPHERE
• High-contrast imaging of HD 163296 with the Keck/NIRC2 L'-band vortex coronograph
• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• Constraining the Orbit and Mass of epsilon Eridani b with Radial Velocities, Hipparcos IAD-Gaia DR2 Astrometry, and Multi-epoch Vortex Coronagraphy Upper Limits
• Astrophotonics: astronomy and modern optics
• A Decade of MWC 758 Disk Images: Where Are the Spiral-Arm-Driving Planets?
• Discovery of a White Dwarf Companion to HD 159062
• Design, pointing control, and on-sky performance of the mid-infrared vortex coronagraph for the VLT/NEAR experiment
• From Dust to Nanodust: Resolving Circumstellar Dust from the Colliding-Wind Binary Wolf-Rayet (WR) 140
• High-Contrast Coronagraphy
• The polarization-encoded self-coherent camera
• High contrast imaging for the enhanced resolution imager and spectrometer (ERIS)
• The First High-Contrast Images of X-Ray Binaries: Detection of Candidate Companions in the $\gamma$ Cas Analog RX J1744.7$-$2713
• ISPY -- NaCo Imaging Survey for Planets around Young stars. CenteR: the impact of centering and frame selection
• An Imaging Search for Post-Main-Sequence Planets of Sirius B
• Revealing the accelerating wind in the inner region of the colliding-wind binary WR 112
• Searching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 Disk