MIRI Coronagraphic Performance (OLD)
The performance of the MIRI flight coronagraphs was tested and verified in the flight model (FM) imager prior to its delivery to be integrated with the full MIRI Optics Module (OM).
The performance of the MIRI flight coronagraphs was verified in the flight model (FM) imager prior to its delivery to be integrated with the full MIRI Optics Module (OM) (Ronayette et al. 2010). A broader discussion on JWST coronagraphy discusses terminology and implementation strategies.
The test arrangement consists of a warm source outside the cryostat with heavy filtering to block room-temperature thermal radiation. A 30 μm diameter pinhole source (much smaller than the FWHM of the diffraction pattern) in the external apparatus was scanned in a raster pattern to measure the response of the coronagraphs.
The coronagraph shows good rejection of the central point spread function (PSF), by a factor larger than 100 on-axis (up to a few hundreds), although the level of rejection is proba- bly limited more by the experimental limitations than by the coronagraph. The scans also showed that the inner-working angle (IWA), defined as the angle with 50% of the maximum transmission, is at 1.3λ=D for the 4QPM units.
Coronagraph Contrast Performance
Boccaletti et al. (2015) describe in detail two models for their analysis: Case A makes relatively optimistic assumptions about the wave front error, while Case B is more conservative. These cases vary the waver front error (WFE) and offsetting accuracy.
Full System Performance
The second part of the simulation includes the detection noise. The figure below displays four cases for various filters. Each subpanel shows the averaged contrast for the PSF (blue line) and the coronagraphic image (red solid line) as well as the 3-σ contrast for the reference star subtraction process (red dashed line) and the ideal noise level if only photon noise dominates (red dash-dotted line). Typical contrasts after postprocessing achieve 104 to 105 for separations larger than 0.5′′–1′′. Note that the radial transmissions of the MIRI coronagraphs are not accounted for in these contrast profiles.
The performance presented in this section is strongly related to the end-to-end optical system assumptions, such as the wavefront error and the whole optical train stability of the telescope. The simulated performance may be conservative, particularly with the development of operations and analysis techniques optimized for JWST.
The current model will have to be updated once the telescope is on orbit and commissioned.