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NIRI Update: guiding issues for NIRI during 2003A

31 Jan 2003

NIRI has been working well recently. NIRI queue observing is scheduled to start 13 Feb 2003. Phase II proposals should be sent to the national project offices for checking as soon as possible (see the 2003A special instructions for deadlines and submission details).

Peripheral wavefront sensor #1 (PWFS1) had a mechanical problem recently and was removed from the telescope for repairs and optical adjustment. Phase II proposals should therefore not request PWFS1 until further notice.

New Shack-Hartmann optics were recently added to the OIWFS for commissioning Altair. With four spots now instead of just one, the on-instrument wavefront sensor readout electronics are rather slow. We are working to improve speed, and therefore performance, but at present OIWFS does not produce better image quality than PWFS2. All projects should therefore make use of PWFS2 until the OIWFS is fully commissioned and functioning.

Elevated read noise has been noticed at times on NIRI and on PWFS2. The limiting magnitude for PWFS2 guiding is approximately R=14 mag, but performance between 13 and 14 mag depends sensitively on how windy it is and how good the seeing is. For now, PIs are encouraged to choose guide stars brighter than 13 mag if at all possible.

The read noise on NIRI is about 50% higher than it should be. This is not an issue for broad-band or high-background imaging, but some narrow-band and low-background exposures may be read noise limited. 60 Hz herring-bone pattern noise is sometimes seen. We are working to eliminate this noise. If you feel it is a concern for your program, please contact your national project office or contact scientist for guidance.

Last update Jan. 31, 2003; Joe Jensen