90Prime Upgrade: Information for 23B Shared Risk Science The 90Prime upgrade had it's 'first light' in February 2023. We continue to commission the instrument, but it is very likely that the upgraded 90Prime will be ready for observing in 23B, We anticipated Shared Risk Science at the beginning of the semester transitioning to normal operations at the end. Here we provide some basic information about the upgrade.

If you are interested, please contact David Sand (dsand@arizona.edu). As the upgraded 90Prime is being developed with a separate dewar, you can also choose to use the current 90Prime for a limited time. Projects that have started with the 'old' 90Prime may complete their data taking with the old dewar and CCD set, but new programs must use the upgraded 90Prime. Scheduling dewar changes between the two systems will be handled by Mountain Operations, and will be worked into the telescope schedule beforehand.

While we anticipate that the newly upgraded 90Prime will be available during the 23B semester, many details are still be worked out as the new focal plane is characterized. Updates will be posted to this website. Here is what you can expect:

• A new focal plane and CCD set that should be cosmetically excellent and have at least the same QE as the current 90Prime. The chips are blue sensitive, just as the current set is.
• The chip gaps are roughly the same as in the old 90Prime. The field of view, pixel size, etc are also nearly the same as the current 90Prime.
• There will be new user GUIs (and backend control software) which will hopefully make the operation of 90Prime easier and less prone to fatal ‘hanging’ errors.
• Other components have been replaced and upgraded, including a new dewar window, shutter, filter wheel components and a new spring mechanism for focus. Some of these upgrades are already in place, and you may not have known!
• Preliminary tests have shown that the new springs improve focus drift during longer integrations. Nonetheless, we plan on implementing a ‘focus maintenance’ code that will both nudge the focus when necessary, and adjust the focus when slewing to a new field. As this has not been tested at all as of yet, it is unlikely this will be implemented in 23B.