CaltechAUTHORS
Published October 2018 | Version Published + Accepted Version
Journal Article Open

Characterizing the Performance of the NIRC2 Vortex Coronagraph at W. M. Keck Observatory

Creators

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon Pomona College
  • 3. ROR icon Jet Propulsion Lab
  • 4. ROR icon Herzberg Institute of Astrophysics
  • 5. ROR icon University of Liège
  • 6. ROR icon W.M. Keck Observatory
  • 7. ROR icon University of California, Los Angeles
  • 8. ROR icon Grenoble Alpes University

Abstract

The NIRC2 vortex coronagraph is an instrument on Keck II designed to directly image exoplanets and circumstellar disks at mid-infrared bands L' (3.4–4.1 μm) and M_s (4.55–4.8 μm). We analyze imaging data and corresponding adaptive optics telemetry, observing conditions, and other metadata over a three-year time period to characterize the performance of the instrument and predict the detection limits of future observations. We systematically process images from 359 observations of 304 unique stars to subtract residual starlight (i.e., the coronagraphic point-spread function) of the target star using two methods: angular differential imaging (ADI) and reference star differential imaging (RDI). We find that for the typical parallactic angle (PA) rotation of our data set (~10°), RDI provides gains over ADI for angular separations smaller than 0farcs25. Furthermore, we find a power-law relation between the angular separation from the host star and the minimum PA rotation required for ADI to outperform RDI, with a power-law index of −1.18 ± 0.08. Finally, we use random forest models to estimate ADI and RDI post-processed detection limits a priori. These models, which we provide publicly on a website, explain 70%–80% of the variance in ADI detection limits and 30%–50% of the variance in RDI detection limits. Averaged over a range of angular separations, our models predict both ADI and RDI contrast to within a factor of 2. These results illuminate important factors in high-contrast imaging observations with the NIRC2 vortex coronagraph, help improve observing strategies, and inform future upgrades to the hardware.

Additional Information

© 2018. The American Astronomical Society. Received 2018 May 28; revised 2018 August 2; accepted 2018 August 14; published 2018 September 14. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work was funded, in part, by a Summer Undergraduate Research Fellowship (SURF) from California Institute of Technology. W.J.X. would like to thank Johanna Hardin at Pomona College for her advice on implementing the statistical models. G.R. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1602444. E.C. acknowledges support from NASA through Hubble Fellowship grant HF2-51355 awarded by STScI, which is operated by AURA, Inc. for NASA under contract NAS5-26555. O.A. is an F.R.S-FNRS research associate. V.B. acknowledges government sponsorship; this research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Facility: Keck II (NIRC2). - Software: VIP (Gomez Gonzalez et al. 2017), QACITS (Huby et al. 2015, 2017), Astropy (The Astropy Collaboration et al. 2018), Matplotlib (Hunter 2007), caret (Kuhn 2008), scikit-image (van der Walt et al. 2014), Mongo (https://docs.mongodb.com/).

Attached Files

Published - Xuan_2018_AJ_156_156.pdf

Accepted Version - 1808.05297.pdf

Files

1808.05297.pdf

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Additional details

Identifiers

Eprint ID
89641
Resolver ID
CaltechAUTHORS:20180914-100923902

Related works

Describes
https://arxiv.org/abs/1808.05297 (URL)

Funding

W. M. Keck Foundation
Caltech Summer Undergraduate Research Fellowship (SURF)
NSF Astronomy and Astrophysics Fellowship
AST-1602444
NASA Hubble Fellowship
HF2-51355
NASA
NAS5-26555
Fonds de la Recherche Scientifique (FNRS)
NASA/JPL/Caltech

Dates

Created
2018-09-14
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Astronomy Department , Division of Geological and Planetary Sciences (GPS)