DEIMOS Troubleshooting > DEIMOS Trouble Recovery > Fix Slitmask Comb Error
DEIMOS control menu > Subcomponents > Start Eventsounds GUIPlease note that not all remote sites are yet equipped with the external speakers required to play the sounds.
We are currently trying to understand why the piezo unit failed; it had functioned well since the instrument was built and was expected to last almost indefinitely. We are not aware of any event which would explain the failure. Unfortunately, due to the long expected longevity and the high cost of replacing the actuator (possibly $10,000 or more), we do not maintain a spare.
Based on measurements made this weekend, the flexure observed over a 360° rotation of DEIMOS on the science mosaic is 45 px in the spectral direction, with substantial hysteresis. This represents a tripling of the flexure measured at commissioning, possibly the result of mechanical decoupling in the piezo unit which is allowing excessive flexure to occur. Such image motion will substantially degrade spectra acquired with DEIMOS unless observers take steps to mitigate the flexure. Possible observing strategies for dealing with the flexure are to keep exposures as short as possible and to restrict observing to the range of DEIMOS rotator angles over which flexure is minimized.
If we are unable to repair the FCS by the May 2009 DEIMOS run, then a potential fallback plan would involve rewriting the FCS software to provide flexure compensation in the spectral direction using the grating tilt stage, which has much coarser resolution than the piezo-controlled tent mirror (1/3 px, vs. 1/100 px). It is not certain that we can provide the manpower to make such revisions, nor is it clear that this would provide suitable flexure compensation. If it succeeds, this approach may provide correction which is significantly worse than the piezo-based system but nevertheless far better than having no FCS at all.
# slitmask with specified rotator position PA_targ_name 00 24 00.00 +16 00 00.00 2000.0 rotdest=123.45 rotmode=pa # target observed at parallactic angle VA_targ_name 12 34 56.78 +01 23 45.67 2000.0 rotdest=0.0 rotmode=vertical
DEIMOS Utilities > Plotmaskfrom the DEIMOS background menu.
DEIMOS Utilities > QuickSlit
gmov 100 200 300 400type
gmov 100 200 310 400
guidermon threshwhere thresh is the threshold at which to generate warnings. The appropriate value of the thresh parameter will depend on the brightness of the guider star and the guider integration time. A reasonable value would be 50% of the starting S/N.