Announcement to NIRI Users in Semester 2001A and 2001B

Matt Mountain, Director

During our initial acceptance tests of NIRI on Gemini North, it was found that NIRI exhibited "flexure", or image motion instability problems that were far larger than expected and outside the original NIRI science requirements. The University of Hawaii's Institute for Astronomy (IfA), which is responsible for NIRI, has tried a number of measures to correct this problem. The image motion is caused by a poorly operating cryogenic bearing on the steering mirrors that select cameras within the NIRI cryostat. Though various attempts at correcting the problem have lead to gradual improvements, none of these have achieved an acceptable performance, and the IfA has concluded that further incremental changes are not likely to fully solve the problem.

At a meeting between Gemini and the IfA on 30th April 2001 it was decided that:

• Both the IfA and Gemini accepted that further commissioning of NIRI would be suspended, and that priority would instead be directed at fixing the image motion problems with NIRI that will require the IfA to redesign and re-engineer the steering mirror responsible for the majority of the flexure.
• The IfA believes that it should be possible to have a viable alternative mechanism ready for installation into NIRI by August 2001.
• With NIRI in its current state it is unclear at this time which programs could be effectively post-processed to remove the effects of flexure. Wide-field imaging programs using the F/6 camera, and possibly F/14 used at thermal wavelengths, may be able to deliver high-grade science observations.

Consequently, the Observatory has decided to inform the affected PIs, National Gemini Offices and National TACs that it will be canceling or suspending all NIRI Queue programs for Semester 2001A until we can determine which programs can be undertaken. (The individual NTAC's, not the Gemini Observatory, can recommend whether programs lost in 2001A should be reinserted into the proposed 2001B schedule.)

In the interim, the Gemini Observatory will proceed with a number of approved System Verification programs, making the resulting data available to the community, to determine which programs can be successfully undertaken before the NIRI flexure problem is fixed. The newly released Observing Tool will be used to define these programs as part of the System Verification process.

The IfA and the Gemini Observatory will proceed on the assumption that NIRI will be available for Semester 2001B, though NIRI will not be formally scheduled before September 2001.

In the event that there is a delay in the NIRI re-engineering of the steering mirror, the Gemini Observatory, in consultation with the IfA will be prepared to support early queue use of NIRI in 2001B for a restricted number of programs that the Observatory judges can be successfully undertaken with NIRI in its current state.

3 May 2001