HCI NIRISS Limiting Contrast

Treatment of limiting contrast (Climit) is based on current information about telescope aberrations and the expected performance of JWST NIRISS AMI.

See also: NIRISS Aperture Masking InterferometryNIRISS Bright LimitsNIRISS Non-Redundant Mask

Limiting-contrast, Climit(s)is the companion-to-host flux ratio of the minimum detectable companion. It is the detection limit and the best that can be done.

The article HCI Contrast Considerations provides a general treatment of "contrast" (C), including Climit(s).

Climit(s) is a function of essentially everything related to high-contrast imaging (HCI): myriad eclectic technical factors and procedures, end-to-end. Figure 1 shows the estimated limiting contrast ratio for a 3-sigma detection of a faint companion near a bright host star as a function of their apparent separation (s) in mas, as measured from in-flight data during JWST commissioning (Sivaramakrishnan et al. 2022).  If the user's operating point (sCflux) lies above a color curve, that source is detectable. Users may be able to extrapolate estimates of Climit(s) using the Exposure Time Calculator (ETC) and other proposal tools.

Figure 1. NIRISS AMI limiting contrast example

Example 3-sigma contrast curves for three medium-band AMI filters from early analysis of commissioning data (108 photons collected). F277W, which was not tested during commissioning, should have a limiting contrast slightly less than F380M.


Sivaramakrishnan, A., Tuthill, P., Lloyd, J. P., et al., 2022, arXiv:2210.17434
The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope – IV. Aperture Masking Interferometry.

Latest updates
    Updated to use in-flight measurements from JWST commissioning.

  • Updated links, including to the new imaging roadmap article. Simplified and clarified text.
Originally published