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4.5 How to Observe with Multi-slits

• At the beginning of the run:
  • Determine the offset between the rotator angle read-out and the actual position angle (PA) on the sky by inserting the 1.0 arcsec wide long slit and running a star east and west along it. This offset may be as large as 1.

• For each slit mask:
  • Go to the zenith.
  • Insert the new slit mask.
  • Rotate the spectrograph to the new PA + offset.
  • Go to the setup position.
  • Move the slitlet mask ``in". Find the setup holes using the backlight of the sky, or, if needed, with the low dome lights turned on. (Remember to turn them off, though!) Mark them using the leaky cursor dots.
  • Move the slitlet mask out and identify the two setup stars. (The separation and angle will help identify which stars are the right ones.)
  • Center the two setup stars on the leaky cursor dots, and tweak the rotator angle if needed.
  • Put the slitlet mask ``in" and center the telescope on the stars. Tweak the rotator angle if necessary.
  • Move to the object field:
    • Method 1: If you have a CHECK STAR in your program field, then: Simply zero the telescope coordinates at the setup position, and move to the coordinates of the program field. Initiate guiding, and center up using the check star.

    • Method 2. If you have NO CHECK STAR in your program field, then: Initiate guiding at the setup field and center up carefully. Move to the object field by offsetting the amounts specified on the output of the multi-slit program.

      Of the two, Method 1 is STRONGLY recommended.

  • Move the rear slit viewer out.
  • Begin the exposure.
  • After each exposure on the field, consider repeating the tweaking up.