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Field-slit Mapping

The mapping of the GMOS-S IFU was modified to allow use of the Nod & Shuffle technique for accurate sky subtraction at the expense of a slightly reduced field-of-view and the loss of the smaller, "sky" field. For the IFU, the shuffle distance should be set to 256 rows.

For both the GMOS-N and GMOS-S IFU the throughputs of the fibers in the Red slit are higher and more uniform that those in the Blue slit (see below), so observers desiring one-slit mode should choose "IFU Right Slit (red)" for the Focal Plane Unit in their science programs.



GMOS-N IFU Field-to-slit mapping

GMOS-S IFU field mapping

The relationship between the IFU fields and the layout on the detector for the GMOS-N IFU is further demonstrated with some example data on NGC 221 (M32) below. These data were taken in two-slit mode using the B600 grating, the g filter, and a central wavelength of 475 nm. The obvious step between the halves of the object field is a known flat-field effect (the right slit has higher average throughput than than the left slit) that can be corrected.  It was left in for this example so that the halves could be distinguished more easily.