DEIMOS
Slitmask Alignment Afternoon Setup Checklist

Purpose

This checklist describes the procedure for you to follow during the afternoon in order to prepare for aligning multiobject slitmasks on DEIMOS, assuming you are:

Procedure

The DEIMOS development team at UCO/Lick has delivered a sophisticated and highly automated slitmask alignment software package which makes the procedure relatively quick and painless. In order for the automated procedure to succeed at night, it is necessary for the observer to perform some rudimentary calibration procedures in the afternoon.

Afternoon Calibration

The goal of this procedure is to tune parameters of the optical modeling algorithm in order to get the correct mapping from physical position on the slitmask to CCD pixels. Only one DEIMOS image must be acquired to complete the calibration.
  1. Select alignment mode. Determine the spectrograph configuration which will be used for slitmask alignment imaging. Options are:
    • Zeroth order imaging. This is the preferred option, since moving the grating to the zeroth order position is much faster than switching to the mirror. This method may not work well if the alignment stars are very faint (R > 20).
    • Mirror imaging. This is the fallback option if the alignment stars are very faint, or if seeing/transparency conditions are poor.
  2. Configure DEIMOS. Insert the slider which will be used for imaging your masks. (Note: while it's not necessary to use a single slider for all of your slitmask alignment imaging, doing so will simplify the process; we assume the one-slider case here.) For zeroth order imaging, the steps are:
    • Open the Gratings Panel by double-clicking on the Grating box on the main Dashboard GUI.
    • At the left-hand side of the Gratings Panel, click on the name of the grating you will use with this slitmask to move it into position.
    • Once the grating is in position, click on the GO ZERO button at the right-hand side of the GUI to move the grating to the imaging position.
    For the mirror, simply select Mirror from the Grating box on the main dashboard GUI.
  3. Acquire slitmask images. Obtain direct images of all of your slitmasks so that you can verify them and calibrate xbox:
    1. Configure the spectrograph with your primary grating for the night.
    2. From the DEIMOS Workspace Menu, select DEIMOS Utilities > Slitmask Imaging Toool to launch the widget.
    3. Select all masks to be observed using this grating.
    4. Click GO to acquire direct images of the masks.
    5. If the secondary slider will also be used, insert this slider, select the masks to be observed with it, and click GO to acquire images with the other slider.
  4. Configure xbox. In this step, you will tune the parameters of the DEIMOS optical model so that the software can predict the pixel location of your alignment boxes based on the information in the slitmask design file.
    1. From the instrument menu, select IRAF/IDL --> cl ds9 (IRAF)
    2. Run IRAF and an associated ds9 window by typing xiraf and load packages keck and deimos.
    3. In IRAF, execute the command cdata to take you to the current data directory.
    4. Next, issue the command 
      	tune_qmodel image
      where image is the name of your alignment image. The program will display the alignment image on ds9 and mark the (inaccurate) predicted locations for the alignment boxes in red.
    5. When prompted by the software, place the cursor in the exact center of any one of the alignment boxes on the image display and press any key. The program will then adjust the qmodel parameters mu and roll3 in order to achieve agreement between the predicted and indicated positions for this alignment box. The resulting locations of all alignment boxes will then be marked on the image in green.
    6. The script will now run xbox for you in practice mode. Verify that all of the alignment boxes on the displayed image are properly found. If so, then the optical model is properly tuned and xbox is ready for action.
    7. Verify masks. Run xbox in practice mode on all of your slitmasks to verify that the masks were cut correctly and that the software predicts the correct box location in each case. (NOTE: it is essential to run this on ALL of your masks to ensure that they have the correct information in their image headers!) If it fails on certain masks, use the check_boxes command in IRAF to show where xbox is looking for boxes and try to determine why they are not being found. Likely reasons are:
      • Box falls in the gap between two CCDs.
      • Box lies on a bad column.
      • Box was placed too close to the edge of the field of view and was removed.
      • The information on slitmask design in the image header is corrupted.
    For problem masks, use check_boxes to generate a file of box positions and feed this as an input file to xbox.

Return to the Afternoon Checklist.

See Also

Go to: DEIMOS Home Page - Instruments Home Page - Keck Home Page
Last modified: Sat Nov 1 20:08:32 HST 2008