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Optical Layout

GMOS optics
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The GMOS optical train is presented in this schematic. One of six available gratings or the imaging mirror is located at the single fold in the optical path. Three 2048x4608 CCDs with 13.5 µm pixels are used as the detector, providing 0.073" pixels. The wavelength range of the optical design extends from 0.36 to 1.10 µm. The CCDs in GMOS North are optimized for the red end of the optical wavelength region, while the CCDs in GMOS South provide better blue and UV sensitivity. It is worth noting however that the primary and secondary optics at both Gemini telescopes have been silver coated, which limits the throughput in the blue for both GMOSs.

GMOS Mechanism
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The forward slit environment of GMOS is fairly complex, since it houses a large number of masks (up to 18 at one time) and the Integral Field Unit in a "jukebox" changer, an on-instrument wavefront sensor used for guiding, and includes the capability to hold an atmospheric dispersion corrector (no current plans for installation). The spectral resolving powers available range from about 670 to 4400 with a slit width of 0.5 arcsec, and 8800 with the narrowest, 0.25 arcsec slit - note, however, that in normal seeing conditions slit losses will be very large for the narrowest slits.

GMOS mechanical layout
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A central truss system is used to suspend the optical elements as well as the CCD dewar from the Instrument Support Structure (ISS). A grating turret with micropositioners behind each grating is used to switch between gratings remotely. Note that although there are six gratings available for both GMOSs, only three can be mounted in the instrument at one time (plus the imaging mirror). Finally two filter wheels mounted on a separate structure and measuring ~1 m in diameter house up to 24 filters for various broad-band and narrow-band imaging and spectrum order sorting functions. The available set of GMOS North filters and GMOS South filters are slightly different.

Last update: October 20, 2006; Kathy Roth
Previous version: June 15, 2006; Bryan Miller