WFIRST-AFTA Coronagraphic Operations: Lessons Learned from the Hubble Space Telescope and the James Webb Space Telescope
- John H. Debesa, Marie Ygoufa, +8 authors Roeland van der Marela
The NICMOS coronagraphic imaging mode has been fully reactivated following SM3B, performing slightly better than during Cycle 7. The diffractive rejection is essentially unchanged (to first order) from Cycle 7 except there is a shift in the mean position of the cold mask which gives better second-order rejection on the downsloping diffraction spikes and slightly worse on the upsloping diffraction spikes. A target can be positioned within ~0.08 pixel (~5.8 mas) of the coronagraphic hole low-scatter position, with a repeatability of ~0.04 pixel (~2.9 mas) for two visits executed within the same orbit, with a roll between visits. The coronagraphic focus was checked and no adjustment was needed. The Cycle 7 coronagraphic focus position is still the best focus. A slight adjustment was made to the PAMC tilt to remove some coma that was not present during Cycle 7. The “hole 32x32 pixel subarray” field-of-regard (FOR) was adjusted by a few pixels in each direction due to displacement of the hole image on the detector caused by the warm up at the end of Cycle 7 and subsequent cool down following SM3B. A new ACQ FOR “gain” table (flat field) was installed to handle hot and cold pixels, allowing Mode-2 acquisitions for targets from H=4 to 17. The coronagraphic hole low scatter point, the “sweet spot,” was checked and a slight adjustment was required to achieve light suppression about the coronagraphic hole comparable to or slightly better than that achieved during Cycle 7.