CFHT, Instruments, Spectroscopy, Gecko: The Coudé f/4 Spectrograph

A few things the OA needs to know about Gecko/CAFE


  1. Dewar fills are MANUAL
  2. Dewar needs to be filled as soon as possible when OA gets to the summit (dewar/CCD need time to settle before taking exposures), and after all Gecko calibrations have been taken in the morning
  3. Temperature must be obtained from the Gecko session before fills
  4. Check the vacuum before performing a fill. A good vacuum should have the needle pegged below the zero tick mark on the vacuum gauge readout. Should the needle on the readout stray above the 1 mTorr tick on the scale, someone must be notified BEFORE filling.
  5. Due to possible electronic noise, the vacuum gauge should be turned off for checkouts and observing.

The agitator should be turned ON (by an Instrument Group person) at the beginning of a run, kept running the whole run, and turned OFF at the end of the run. The OA does not need to turn the Agitator ON or OFF, but every night, the OA should check that the fiber agitator is working and that it is not loose at the slicer end (in the Slit Room; the fiber gets from the Cass environment to the Coude Room throught the Slit Room).

The Exposure Meter should be turned ON by the OA every night (outside the Coude Room, in the outer Clean Room area; there are instructions next to the Power Supplies for the Exposure Meter) just before the first science exposures, and turned OFF at the end of the night. The modules in the control room also need to be turned ON; they can be kept ON for the whole run.

If observers want to take darks during the day, they can. The only restriction is that no one should go in the Inner Coude Room when the darks are taken. Dome lights can be turned ON when darks are being taken with Gecko.

When observers are doing calibration frames (Th/Ar lamp or Flat Field lamp) between science exposures, the CAFE TV camera is disabled (so that it does not get burned accidentally by the lamps...) and the CAFE TV screen signal is lost; therefore, the observer should tell the OA when taking calibration exposures, so that the OA can stop the guiding. If the OA was guiding on a object and the observer forgot to mention they were switching to calibration frames, the guiding will be lost.

Procedure to be used by the Observing Assistant to acquire objects and guide.

  1. Select a star
  2. Go Direct - or use other slew method
  3. Select Cass Camera (normal)
  4. Cass (X,Y)=(-5,4)
    NOTE: TCSIV sometimes moves bonnette to -150,0
  5. TV hot spot should be (X,Y)=(289,232) [value updated March 4, 2001, and valid for the spare fiber]
    NOTE: TCSIV changes this when you slew, unless it is set as instrument hot spot
  6. Push star to box
  7. Select CAFE camera - same as TV hot spot 289,232
  8. Wait for bonnette to move to -120, -120, and Mirror 6 to get out of the way
  9. Turn up camera gain
  10. Push star to box and start guiding


The field of view is 40 arcsec in diameter. The small (inner) box is 2 arcsec wide; the big box (outer) is 6 arcsec wide.

The camera sees light picked-up from the science beam (on-axis guiding) by a circular pellicle; this pellicle does not take the whole TV screen.

Orientation of the cameras

RED MESSAGE about "Old det_z value"
When the Gecko user focuses the spectrograph (not the telescope), the "z" value for the detector (that is, the focus value), is going to change and a red message will appear saying something like:
RPM/2.7: Old det_z value was -11885.8; New value is -11901.6972943.
This is not an error message, just an information message (it shouldn't be in red). It can be ignored.

Aaaaahhh! I shouldn't be reading this secret stuff! Get me back to the Main page!
Send comments to manset -=AT=-
Copyright © 2004. CFHT Corporation. All rights reserved.