JWST High-Contrast Imaging

High-contrast imaging (HCI) with JWST will allow observers to obtain images of faint sources located near bright point sources.

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Main articles: NIRCam Coronagraphic Imaging, MIRI Coronagraphic Imaging, NIRISS Aperture Masking Interferometry 
See also: NIRCam Coronagraphic Recommended StrategiesNIRISS AMI Recommended Strategies, MIRI Coronagraphic Recommended StrategiesNIRISS AMI Observations of Extrasolar Planets Around a Host Star


High-contrast imaging (HCI) is used to obtain images of faint sources ("companions") located near bright point sources ("hosts"). Typical hosts are stars and quasars. Companions include exoplanets, circumstellar structures of gas and dust, and luminous feeding zones around supermassive black holes. In normal imaging, a faint companion could be swamped and lost in the noise of diffracted light in one of the wings of the host. HCI strategies—comprising special optics, observing procedures, and post-processing—are designed to reduce the impact of host light at the position of the companion, in order to make the companion detectable against the residual noise.

In HCI, the reduction of wing light from the host occurs in two steps: optical cancellation and image subtraction. Optical cancellation is achieved by special optics, pairs of masks located on the focal and pupil planes. Image subtraction is performed in post-observation processing by differencing a scaled PSF reference image and a science image (see PSF subtraction strategies).

JWST offers 3 HCI designs for optical cancellation: 2 types of coronagraph and one interferometer (see JWST High-Contrast Imaging Optics). Subsets of these designs are implemented in NIRCam, MIRI, and NIRISS: 

Lyot coronagraph (LYOT; 5 implementations in NIRCam, one in MIRI)

4-quadrant phase mask coronagraph (4QPMC; 3 implementations in MIRI)

aperture masking interferometer (AMI; one implementation in NIRISS) 

The instrument-specific modes for HCI, including allowed mask-filter combinations, are described in: 

NIRCam Coronagraphic Imaging
MIRI Coronagraphic Imaging
NIRISS Aperture Masking Interferometry

There are 2 primary performance metrics for HCI: (1) the inner working angle (IWA) and (2) the limiting contrastClimit(s), which is a function of apparent separation (s).

For more detailed information about JWST HCI options, see the references listed below. 



High-contrast imaging articles

JWST User Documentation Home
Acronyms and Abbreviations

Observing modes

MIRI Coronagraphic Imaging
NIRCam Coronagraphic Imaging
NIRISS Aperture Masking Interferometry

Instrument

MIRI Coronagraph Masks
NIRCam Coronagraphic Occulting Masks and Lyot Stops
NIRCam Filters for Coronagraphy
NIRISS Non-Redundant Mask

Detector

Understanding Exposure Times
MIRI Detector Readout Overview
MIRI Detector Subarrays
NIRCam Detector Readout Patterns
NIRCam Detector Subarrays
NIRISS Detector Readout Patterns
NIRISS Detector Subarrays

Operations

MIRI Coronagraphic Imaging Target Acquisition
NIRCam Coronagraphic Imaging Target Acquisition
NIRCam Coronagraphic PSF Estimation
NIRCam Coronagraph Astrometric Confirmation
NIRCam Small Grid Dithers
NIRISS Target Acquisition
NIRISS AMI Dithers

Performance

MIRI Bright Source Limits
MIRI Sensitivity
MIRI-Specific Treatment of Limiting Contrast
NIRCam Point Spread Functions
NIRCam Bright Source Limits
NIRCam-Specific Treatment of Limiting Contrast
NIRCam Sensitivity
NIRISS Bright Limits
NIRISS Sensitivity
NIRISS AMI-Specific Treatment of Limiting Contrast

Recommended strategies

MIRI Observing Strategies
NIRCam Coronagraphic Recommended Strategies
NIRISS AMI Recommended Strategies

Science use cases

MIRI and NIRCam Coronagraphy of the Beta Pictoris Debris Disk
NIRISS AMI Observations of Extrasolar Planets Around a Host Star

Astronomer's Proposal Tool

JWST Astronomers Proposal Tool Overview
JWST High-Contrast Imaging in APT
JWST APT Coronagraphic Sequence Examples 
MIRI Coronagraphic Imaging APT Template
NIRCam Coronagraphic Imaging APT Template
NIRISS Aperture Masking Interferometry APT Template
APT Target Acquisition
APT Special Requirements

Exposure Time Calculator

JWST Exposure Time Calculator Overview
JWST Coronagraphy in ETC
JWST ETC Coronagraphy Strategy
JWST ETC Target Acquisition
JWST ETC to APT Interface Support Information

Proposing tools

JWST Coronagraphic Visibility Tool Help



References

Beichman, C. A., et al. 2010, PASP, 122:162
Imaging Young Giant Planets from Ground and Space

Boccaletti, A. et al. 2015, PASP, 127, 633
The Mid-Infrared Instrument for the James Webb Space Telescope, V: Predicted Performance of the MIRI Coronagraphs

Greenbaum, A.Z., Pueyo, L., Sivaramakrishnan, A. et al. 2015, ApJ, 798, 68
An Image-Plane Algorithm for JWST's Non-Redundant Aperture Mask Data




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