Data access for MIRI observations of coronagraphic PSF reference star-associated background targets has been updated to match the treatment of their corresponding PSF reference star observations. Both type of observations now have zero exclusive access period. All science target-associated data products still have the default exclusive access period.

PSF reference observations are not by themselves of scientific interest, but rather are used to calibrate out the PSF of a separate science target in order to reveal astrophysical signal in its vicinity. During MIRI commissioning, it was shown that a contemporaneous background was needed to remove telescope stray light from the PSF reference observations.

The change to zero exclusive access period applies both to future observations as well as to those currently archived on MAST. This change has been propagated to higher-level pipeline products that use these backgrounds, so that background-subtracted and calibrated PSF reference star observations are now publicly available on MAST, as originally intended.

Science target-associated background observations are also unaffected by this change, with the caveat that APT associates backgrounds with targets at the “Target” level, not at the “Observation” level. This means that if the same background-type target is designated as the background for both the science and PSF reference stars, then all observations of that background target will have zero exclusive access period.

MIRI users who have questions or concerns about this change are encouraged to reach out to the JWST Help Desk, using the MIRI card.