HCI NIRCam Limiting Contrast

Examples of NIRCam's high contrast imaging (HCI) limit, Climit(s), are based on current information about telescope aberrations and the expected performance of NIRCam Coronagraphy.

See also: NIRCam Coronagraphic Imaging, NIRCam Bright Source Limits, NIRCam Coronagraphic Occulting Masks and Lyot Stops, NIRCam Filters for Coronagraphy

Caution on Limiting Contrast

The information contained in this article is presented as a general guide based on pre- and post-launch experience. The ultimate contrast achieved in a science observation will depend on many technical factors, including but not limited to: the relative brightness, spectral type, and angular separation of the target and reference stars; the stability of the optical wavefront throughout the observing window, the exposure parameters, and the image-processing strategy.

The article HCI Contrast Considerations provides a general description of contrast (C), including Climit(s), the ratio of the fluxes of the faintest detectable companion and its host star. The top-left panel of Figure 5 in NIRCam Coronagraphic Imaging, which is adapted from Figure 6 of Beichman et al. (2010), shows pre-launch predictions of Climit(s) for NIRCam's three round occulters (MASK210R, MASK335R, MASK430R) and two bar occulters (MASKSWB and MASKLWB) paired with filters F210M, F335M, F430M, F210M, and F430M, respectively. The right panel of the same figure shows measured Climit(s) curves obtained from post-launch commissioning images using MASK335R, F335M, and different techniques for subtracting the coronagraphic point spread function (PSF). The measured curves indicate that the pre-launch predictions were fairly accurate at small angular separations from the host star but overly optimistic at large separations in the background and/or detector readout noise limited regime. 

Figures 1 and 2 below show additional examples of measured Climit(s) compared with more recent and improved NIRCam coronagraphic models. In each case, a companion is considered detectable if its combination of angular separation and flux (s, Cflux) lie above the Climit(s) curve for a given occulter and filter.

Figure 1, adapted from Carter et al. (2023), shows the measured Climit(s) using for MASK335R and filter F356W derived using the RDI (reference star differential imaging) and ADI (angular differential imaging) PSF subtraction strategies (see NIRCam Coronagraphic PSF Subtraction Operations for explanations of each). These measured curves are compared with the corresponding predicted curves derived from the PanCAKE simulation tool (Carter et al. 2021). These curves reflect the following technical factors:

  • ADI at roll angles differing by 10°
  • Random position errors of 10 mas and and wavefront errors of 10 nm introduced between rolls
  • A 5σ false alarm probability of 6×10–7. (Normally distributed errors with zero mean are assumed after image differencing.) 
  • Estimated JWST aberrations of Beichman et al. (2010).

Figure 1.  NIRCam HCI limits for MASK335R and F356W

Click on the figure for a larger view.

Measured 5σ contrast limits for the NIRCam MASK335R occulter and F356W filter using the ADI and RDI PSF subtraction strategies. The data were obtained from Early Release Science program 1386. The light blue curves show the corresponding model curves generated using the PanCAKE simulation tool.  (Adapted from Carter et al. 2023.)

Figure 2, adapted from Figure 7 of Ygouf et al. (2024), shows the 3σ contrast curves measured for the MASK430R occulter and the F356W and F444W filters. The measured curves are compared with the corresponding predicted curves derived from the pyNRC package (Leisenring 2025). Although MASK430R has a larger inner-working angle (IWA) than that of MASK335R, the contrast limits for separations > 1 arcsecond are significantly deeper. As in Figure 1, the measured and simulated contrast curves are very well matched.

Figure 2. NIRCam HCI limits for MASK430R using F356W and F444W

Click on the figure for a larger view.

3σ contrast curves (left) and mass detection limits (right) for the Fomalhaut system for the NIRCam MASK335R occulter with the F356W and F444W filters. The top panels (a, b) are simulations performed with the pyNRC package (Leisenring 2025). The bottom panels (c, d) are measured contrast curves derived from Cycle 1 GTO Program 1193. The contrast curves in panel (c) are the deepest achieved so far with NIRCam coronagraphy. The wiggles in the flat part of the curves (separations > 3 arcsec) are due to background objects. The mass detection limits in panel (d) are displayed only for F444W, which is the most sensitive filter for planet detection, as demonstrated in panel (b). At these wavelengths, wavefront errors < 5 nm between the science and reference star observations are inconsequential beyond 1 arcsecond from the star. (Adapted from Figure 7 of Ygouf et al. 2024)

The estimates of Climit(s) obtained with the Exposure Time Calculator (ETC) are adequate to prepare proposals.


References

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

Carter, A. L., et al. 2021, Proceedings of the SPIE, 18230H 
Simulating JWST high contrast observations with PanCAKE

Carter, A., et al. 2023, ApJ Letters, 951, 1 
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High Contrast Imaging of the Exoplanet HIP 65426 b from 2-16  μm

Girard, J. H., et al. 2022, Proceedings of the SPIE, 121803Q   
JWST/NIRCam Coronagraphy: commissioning and first on-sky results

Leisenring, J., 2025 / pyNRC
pyNRC: a JWST NIRCam ETC and Simulator

Perrin, M., et al. 2018, SPIE, 1069809
Updated Optical Modeling of JWST Coronagraph Performance, Stability, and Strategies

Ygouf, M. et al., 2024, AJ, 167, 1 26 
Searching for Planets Orbiting Fomalhaut with JWST/NIRCam



Notable updates
    • Heavily edited and reorganized text
    • Added new reference

    • Updated Figure 1
    • Added Figure 3 based on Ygouf et al. (2024)
    • Added new references


  • Added a NIRCam in-flight contrast example (Fig. 2)
Originally published