Purpose

This checklist describes the "emergency" LRIS-style procedure for aligning multiobject slitmasks on DEIMOS when the image header is faulty and does not contain the typical information on the positions of the alignment boxes.

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Setup

The following steps would ideally be done in the afternoon in order to save time on sky; however, they can also be done during the night.

1. Acquire direct slitmask image. This can be done in the afternoon via the DEIMOS Slitmask Imaging Widget, or can be an alignment image acquired on-sky as part of the fine alignment procedure.
2. Create box coordinates file.
   • In IRAF, use the check_boxes command to mark locations of the alignment boxes. Launch the program via:

     	check_boxes image maskname.box autogen-

     where image is the name of the image to display and maskname is the name of the slitmask.
   • When check_boxes displays the image, center the cursor within an alignment box (use the arrow keys for fine-tuning) and press the m key to mark the box. Repeat for each box.
   • Press q to save the coordinates to the file.

Alignment Procedure

This is essentially identical to the standard slitmask alignment procedure, with the exception of the step indicated in red below.

1. Focus telescope and complete fine alignment.
2. Complete fine alignment.
   In this step, you will refine the positions of the stars within their respective alignment boxes to achieve optimal centering of the slitmask.
   • Have the OA select a guide star and begin guiding. Ensure that the guide star selected is not too close to the edge of the guider field, since small offsets may still be required.
   • Start a 20-40 sec direct exposure through the slitmask.
   • In your IRAF window, type epar xbox to edit the parameters for the xbox task. Set the input parameter to the name of the box coordinates file you generated earlier with check_boxes.
   • In your IRAF window, type do_xbox anytime before the image has been written to disk. The script will wait for the current image to be written, will determine the name of the image, and then will beep to indicate that it's time for you to wake up and run xbox.
   • To run xbox on your image:
     • For each alignment box, xbox will plot row and column cuts through the box to show the quality of the centering. Press:
       • q if the centering is acceptable
       • i to ignore the current box if the star is not seen or the object is inappropriate (bad coordinates, galaxy, double-star, etc.)
       • spacebar to reset the sky level if it was incorrectly measured by the program (sky will be reset to the current y-position of the cursor)
     • When done reviewing all boxes, xbox will plot a residual map. If any discrepant points are noted, press d to delete the offending point and f to re-do the fit. Press q when the fit is acceptable.
     • The program will report the suggested moves in rotation and position, as well as the uncertainties (in parenthesis).
     • Answer y to the prompt:

            [CONFIRM]  Send DCS commands? (y/n) [y]:

     • Accept the suggested rotator move if it is significant compared to the uncertainty.
     • Perform another alignment iteration if:
       • a rotator move was required, or
       • either the north or east offset was > 0.2 arcsec (or whatever your personal tolerance is)
3. Set up for spectroscopy.
   • Reconfigure the instrument for spectroscopy:
     • Set grating to the appropriate central wavelength (if using zeroth order imaging you can use the GO BACK button to return to original setting).
     • Set filter to the desired position for order blocking.
     • Set dewar focus as appropriate for the selected filter.
   • Set the detector parameters appropriately:
     • Set ReadOut to Spectral.
     • Set ObsType to Object.
     • Set ExpTime as desired for spectroscopy.
4. Wait for FCS to settle. Do not start your exposure until the FCS GUI shows the FCS status as locked, or it may be smeared.
5. Expose!

See Also

• Standard Slitmask Alignment Procedure
• DEIMOS Slitmask Alignment Afternoon Setup Checklist
• DEIMOS Slitmask Imaging Widget