Simulations of JWST MIRI 4QPM coronagraphs operations and performances

We present the results of ongoing coronagraphic simulations aimed at designing strategies for optimizing oper- ations of the coronagraphs in the mid-infrared instrument (MIRI) on-board the James Webb Space Telescope (JWST). In particular, the adverse effects on the point spread function caused by the phase mask coronagraphs and the observatory slew accuracy are known to limit our ability to position stars at the center of the coron- agraph. Here, we investigate these two effects on our ability to perform target acquisition (TA) and consider different scenarios involving single and multiple acquisitions to mitigate them. We assess the performance of the coronagraphs under various slew accuracy models as well as noise sources. In general, we find that scenarios that require fewer acquisitions yield final positions with smaller dispersions but larger offsets. Our Single TA scenario yields the best repeatability for all three slew accuracy models that we considered although a dual Twin TA strategy generally yields more accurate centering. We also investigate the use of the contamination control cover (CCC) inside MIRI during TA of bright objects, and ways to mitigate the resulting latent images when the CCC is not used. Our results are expressed in terms of achieved contrast with simple, single reference star subtraction. Given our preliminary prescription for latency, our simulations suggest that the CCC need not be used except for very bright sources; detailed guidelines will require additional information on the latent image decay time scale. Furthermore, we find that contrast is dependent on the observatory slew accuracy at any wavelength. The highest contrast is achieved with the highest slew accuracy model, although the background photon noise limits the contrast at longer wavelengths.