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Integral Field Spectroscopy

The integral field mode of GMOS provides the ability to perform spatially resolved spectroscopy. This mode uses a lenslet array (containing 1500 elements) in the pre-slit environment to slice the focal plane into a multitude of small components. Each lenslet is coupled to a fiber. The fibers are organized into a linear array terminating at the nominal location of the slit of the spectrograph. It is possible to reconstruct an image at a particular wavelength, or extract a spectrum from any point in the field of view. The science field of view is 35 square arcsec (5"x7") and is sampled by 1000 elements. The sky is sampled by the remaining 500 elements which are located ~1 arcmin away from the science field of view. The GMOS-N IFU has been available since early 2002. The GMOS-S IFU has been available for science use since April 1, 2004.

In the future the IFU mode may be commissioned for use with Adaptive Optics. The mode is well suited for AO since it makes optimal use of the AO-corrected field, unlike a slit which blocks much of the corrected field. Currently the Altair AO facility instrument on Gemini North only transmits light longward of 835 nm to the science instruments, so the GMOS-N would only have access to a limited wavelength range. Plans to upgrade the CCDs on both GMOSs to more red sensitive detectors may make commissioning GMOS-N with AO a more attractive option.

Because there is no Atmospheric Dispersion Corrector installed in either GMOS-N or GMOS-S, observers of extended sources should be aware that when observing in the blue or with the one-slit mode (to obtain wider wavelength coverage) different wavelengths may fall on different lenslets, especially at high airmass. It is possible to correct for this effect in data reduction using the GMOS IRAF package.