Quick Review

  1. Identify Boxes in the afternoon
  2. Retrieve DSS images of guider fields in the afternoon
  3. Focus the telescope using MIRA: if needed
  4. Slew to target and while slewing
  5. Coarse Alignment
  6. Fine Alignment:
  7. Start Spectroscopic Observations .

Slitmask Alignment

This checklist describes the procedure for aligning multi-object slitmasks on LRIS using the Slitmask Alignment Tool (SAT). Released for use in January 2011, the SAT provides a complete set of tools for aligning slitmasks. Given a properly-formatted starlist, the SAT predicts guide star locations which may be used to coarse align a slitmask. When fine-tuning mask alignment, the SAT displays graphical fits to objects/boxes in an all-in-one display and makes recommendations for telescope offsets and rotation. Mask alignment with the SAT is more efficient than the traditional command-line and IRAF-based scripts. Below are screen shots of the tool for the three primary observing uses:

To launch the SAT:

WARNING: The coordinates in the starlist must be the coordinates for the center of the mask, accounting for all relative shifts that may have been applied while designing the masks.

Focus telescope

Focusing the telescope before aligning a slitmask is recommended. The focus is strongly dependent on the LRIS physical rotator position and the telescope elevation. It is generally recommended to re-focus the telescope when the telescope elevation angle has changed by 30° or more, and/or the instrument's physical rotator position (displayed as drive on the FACSUM display) has changed by 40° or more. In practice, this often means that refocusing is done for each slitmask, since each mask may have a different rotator position.

To complete the focus:

  1. Highlight the target in the MAGIQ target list using the middle mouse button, and ask the OA to slew to the new highlighted target.
  2. Ask to OA to run MIRA in the neighborhood of your target.

Slew to Target

  1. While slewing
  2. When the OA tells you that your target is on LRIS, check the following information on FACSUM to verify that your position is correct:

Coarse Alignment

In these steps, we put the stars into the alignment boxes.
  1. Ask the OA to set secPer to 5 or less in order to provide frequent "full-frame" offset guider image updates. The SAT needs to read a full-frame guider image and if full-frame images are not updated frequently, this step will take a long time.
  2. On the SAT, click the Coarse Alignment tab
  3. Click Grab Guider Image, which:
  4. Identify DSS stars in guider image.
  5. Click on an object in the guider image (at right). The SAT will then:
  6. If the highlighted DSS star is not correct, select a different star by either clicking in the DSS image on the appropriate star or selecting the star in the guide star list.
  7. Click Move Telescope
  8. Optional: Confirm guider move and repeat above steps if necessary.

Fine Alignment

In this step, we refine the positions of the stars within their respective alignment boxes to achieve optimal centering of the slitmask.
  1. On the SAT, click on the Fine Align tab.
  2. Confirm that LRIS is configured for imaging:
  3. Click Start Fine Alignment button. The software will then:
  4. Review Object and Box fits, calculated offsets, and move recommendations. For each star the SAT graphs:
    XYFIT codes
    Graphic Description
    white solid line star and box profile
    vertical white dotted line fitted object peak intensity
    green box shows centering of the fitted box
    blue dashed line estimated sky level
  5. If necessary, remove a star from the fitting process by de-selecting the star. Click the button to the left of the offending star's graphs. Some possible reasons to remove a star from the fit are: If you exclude a star from the fit, the offsets will be recalculated with that object ignored. Please see the example image of a star excluded from the fit.
  6. If you want to change a move recommendation, select the Y or N button next to the offset.
  7. Send the Moves


  1. Reconfigure the instrument for spectroscopy:
  2. Set exposure time as desired for spectroscopy.
  3. Expose...phew!

Retrieve all Guider Images

If you adjust the coordinates in your target list, you will need to reclick on Retrieve all Guider Images to ensure your guider images are up to date.

Identify Boxes

Follow these steps to generate the “box files” that record the locations of your alignment boxes. Please note that this procedure is typically completed in the afternoon.
  1. Acquire a set of direct slitmask images via the LRIS Slitmask Imaging Tool, as described here.
  2. Launch the Slitmask Alignment Tool.
  3. Click on the ID Boxes tab on the Slitmask Alignment Tool. Please see the example image of the identify boxes tab.
  4. Click Load Image and select one of your slitmask images. The image will be read from disk and displayed in the GUI.
  5. Locate one of your square alignment boxes on the image. Move the mouse cursor to the center middle of the box.
  6. Press the m key to mark the box. The tool will draw a red square around the box, and will automatically add the new box coordinates to the box file on disk.
  7. Repeat the above step for each box on the mask.
  8. If you need to delete a box, press the d key to remove the box nearest to the cursor position. Again, the software automatically updates the box file stored on disk.
  9. If desired, verify that the box file was written to disk by listing the contents of your data directory and verifying that box files (with a .box suffix) exist.
  10. Repeat the above steps for additional slitmasks.