AAOmega FPI and Gripper fibre surveys
In order to model the gripper distortion with respect to the FPI astrometric reference frame, we need to undertake a series of surveys of the AAOmega fibres positioned on the field plates. We do this with both the FPI camera and the Gripper camera. The process derives a relative distortion map between the FPI and Gripper (the absolute distortion of the FPI gantry is taken out via a different process) assuming that any mismatches are due to the distortion of the gripper gantry. This is also described in a (see the February 2008 AAO newsletter article).
The problem: The problem here is that we need four sets of fibre surveys. These all have to be done in a relatively short space of time (i.e. one day, before the fibres are moved). However, they take a long time to do, particulalry with the FPI, and the astronomer usually cannot get the minimum useful set of data inside a day without help.
The process: A special fibre grid pattern is needed to derive the distortion map. This can be found in the grid directory. However, for the purposes of checking the distortion (rather than deriving a new one), any fibre configuration can be used provided it has a good spread of coverage across the field plate. Briefly the process is as follows:
Park the telescope, zenith is best, and NOT at access park (prime focus).
Survey the field plate fiducials with the gripper
Survey the fibre positions with the gripper
Survey the field plate fiducials with the FPI
Survey the field plate fibres with the FPI
In practise: Follow this procedure. Note that the FPI can be done first if required, as long as FPI and gripper survey pairs are done.
All these files should be saved to a standard location and with a date stamp in the name. Note, the tdfeng save options default to saving to the directory /instsoft/instuser/aatinst/. There is a subdirectory here called newFPI_fibresurveys. Please create a new sub directory in this one with the relevent date information, suggestions are:
Turn on the full tdfeng debug information output (click the bug icon on the tdfeng task bar).
Park the telescope, at zenith is best.
From tdfeng, clear the text in the text box (right-click->clear text)
Force a Gripper field plate fiducial survey (Plates->survey fiducials)
Save the survey text from the text box (right-click->save to file)
Survey the fibre positions (Fibres->suvrey fibre positions), a prompt appears asking for the file name to save the data to.
Tumble the field plate
Now the tricky bit. The FPI gantry cannot see the fibres and fiducials by default, we need to swap the fibre illumination over.
Select Fibres->Back illuminate guide fibres for the plate the FPI is to survey.
From the AAOmega tdfct control change the observing slit to be the one for the field plate the FPI is to survey.
Put the back illumination into always on mode (Parameters->Set/Report task parameters>Gripper gantry task-> Backill_always=1)
Clear the text box again (tdfeng right-click->clear text)
Force an FPI field plate fiducial survey (Plates->survey fiducials)
Save the survey text from the text box, (right-click->save to file)
Survey the fibre positions, with the FPI (Fibres->suvrey fibre positions), a prompt appears asking for the file name to save the data to
Repeat for the other field plate
Repeat all sets with as many different fibre configurations as practical
Email the AAOmega team with the location of the results files (firstname.lastname@example.org)
Sarah Brough (email@example.com)