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NIRI is an near-IR imager/spectrometer operating over the 1 to 5um wavelength regime. The instrument is cryogenic and is cooled by two Leybold closed-cycle cooler units to an IR array operating temperature of around 30-35K. All optical elements inside the NIRI cryostat are cooled and, in general, will reach operating temperatures of around 60 to 80K. Since NIRI is cryogenic, the cryostat is pumped and cryo-cooled to a pressure better than 10^-5 torr.
The optical chain from entrance window to IR detector is as follows:
Mid-IR observing programmes would often benefit from absolute astrometry with subarcsecond accuracy, for example for comparing mid-IR images of galaxy nuclei or star-forming regions with images at other wavelengths. In this page we guide the user through the steps necessary to set up accurate absolute astrometry in the OT. The procedure at mid-IR wavelengths differs from that used in the optical because of low probability that two stars close enough to use the same guide star will be both bright at 10 or 20 microns.
As at near-IR wavelengths, telluric standard star observations are required for mid-infrared spectroscopic observations to cancel telluric (atmospheric) absorption features in the data. The following is a guide to assist in selecting the most appropriate telluric standard stars. Two telluric standard observations must be included in the phase II definition for each observation lasting more than ~30 minutes, one airmass-optimized for measurement before the science target, and one for after the target.
Standard star observations are required for mid-IR imaging observations to allow the calibration of data onto a magnitude or flux scale. The following is a guide to assist in selecting appropriate flux standard stars. Two standard star observations must be included in the phase II definition for each observation lasting more than ~30 minutes, one airmass-optimized for measurement before the science target, and one for after the target. The Gemini staff member at the telescope will select one of these for baseline calibration, which will not be charged to the science program.