WFI Aquisition

Imaging Acquistion Procedures

Simple Preset: WFI_img_acq_Preset

This is the simplest and most commonly used acquisition template which does the following:

points the telescope to the required field
puts the correct filter in the beam
aquires a guidestar

The above example shows a simple preset template to track the target with the V/89 filter. This assumes that your first science exposure will also be taken with the V/89 filter to minimise overheads with changing filters.

Move to Gap: WFI_img_acq_MoveToGap

This template is used when you want to move a bright star into one of the inter-chip gaps, or if you wish to place a particular star on a particular pixel (discerned from the following diagram and table of the WFI mosaic. It invokes the following steps:

points the telescope to the required field
puts the correct filter in the beam
aquires a guidestar
takes an exposure with Exposure time seconds
reads out the CCD and transfers the data
the current coordinates of the target star are entered into a popup window
This must be clearly indicated on the finder chart for SM observations
the desired coordinates of the target star are entered into a popup window
These must be given in the README file for SM observations
you may then select to do one of the following:
- perform the offset and take another image to check the offset (i.e. repeat from step 4)
- perform the offset and move onto the science exposures (i.e. you trust the offset and are not too worried about exact positioning)
- do not perform the offset and move onto the science exposures (i.e. the star will remain where it is in the aquisition image)
- abort the OB
What you choose will depend on exactly how precise you want the positioning to be. Usually the initial offset (first iteration) will put the star within 10 pixels of the requested pixel coordinates. Subsequent iterations will get it within a few pixels, but the chances of it actually falling exactly on the same pixel are not high.

One should allow ~2 minutes + exposure time for each iteration.

P2PP panel with typical parameters

The above example shows an acquisition template to preset the telescope, put the V/89 filter in the beam, start the autoguider and take a 10 second acquisition image. The rest of the information required for this procedure (initial and final x,y coordinates of the star, whether you want to iterate or not) are entered into popup windows.

Move to Pixel: WFI_img_acq_MoveToPixel

This template is used when you want to place a particular star on a particular pixel (discerned from the following diagram and table of the WFI mosaic. It invokes the following steps:

points the telescope to the required field
puts the correct filter in the beam
aquires a guidestar
takes an exposure with Exposure time seconds
reads out the CCD and transfers the data
the current coordinates of the target star are entered into a popup window
This must be clearly indicated on the finder chart for SM observations
the desired coordinates of the target star are read from the template.
you may then select to do one of the following:
- perform the offset and take another image to check the offset (i.e. repeat from step 4)
- perform the offset and move onto the science exposures (i.e. you trust the offset and are not too worried about exact positioning)
- do not perform the offset and move onto the science exposures (i.e. the star will remain where it is in the aquisition image)
- abort the OB
What you choose will depend on exactly how precise you want the positioning to be. Usually the initial offset (first iteration) will put the star within 10 pixels of the requested pixel coordinates. Subsequent iterations will get it within a few pixels, but the chances of it actually falling exactly on the same pixel are not high.