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 Interferometry, NIRISS Bright Limits, NIRISS Non-Redundant Mask

The contrast limit, Climit(s), is the highest detectable host to companion flux ratio.

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 (s, Cflux) 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.

References

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.



Notable 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