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The optical elements of GNIRS (e.g. cameras, gratings, cross-dispersing prisms and slits) are described in detail on the GNIRS spectroscopy pages.
The choice of camera, grating and slit width set the spectral resolution. Not all combinations are viable. Use of the cross-dispersing prism may be toggled on/off (again, only some combinations of prism, grating and camera are viable). Given a specific central wavelength, the choice of "blue" or "red" optimised camera, grating order and order sorting filter is made automatically. A broad-bandpass filter is used with the cross-dispersing prisms.
Note that even though specific capabilities are listed in the ITC, they may not be available in every semester.
Caution: the atmospheric transmission and emission files currently used by the ITC have a resolution of 1nm and therefore produce telluric features substantially broader than the actual instrumental resolution, especially at R=5900 and 18000. The inter-line signal and noise calculations are correct.
The four combinations of well depth and read mode (more specifically, the number of non-destructive reads) define the minimum exposure time, read noise and saturation limit. At this time, there is no checking of saturation or that the specified exposure time is more than the minimum allowable.
Values of the read noise and minimum exposure times are given on the GNIRS science detector page.
Dark current: laboratory characterisation indicates a value of 0.1e-/s at the adopted operating temperature. This may include some internal cryostat background (e.g. a low-level light leak).
GNIRS On-Instrument Wavefront Sensor
At this time, the GNIRS OIWFS is not available. The facility Peripheral Wavefront Sensor is required for tip-tilt image stabilisation.
Last update August 31, 2004; Phil Puxley