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Mask Design Using Existing Object Catalogues

Using dedicated GMOS images (pre-imaging) for designing MOS masks has the advantages of being independent of the accuracy of any astrometric calibration and immune against proper motions of alignment stars or objects. However it also requires more telescope time, and requires time between the start of the semester and the start of the MOS observations for the pre-imaging to be taken and the mask to be designed.

Gemini Planet Imager First Light!