GNIRS Grating Usage: long camera and 32 l/mm

The wavelength coverage is about 0.45um so two grating settings are required to cover the entire window. With a wider slit to reduce slit losses the resolving power is degraded e.g. 0.3 arcsec slit yields R=1700 for an object that fills the slit. One can observe in the M-band with the short camera and the 110 l/mm grating, the maximum exposure time is ~0.5sec with the 0.3arcsec slit; if the objects are sufficiently bright that slit losses are not an issue, use of the long camera allows ~3x longer exposure times (thereby reducing overhead).

Example spectra shown below of a standard star: 4.4 - 5.1um in 1st order

This mode gives approximately the same resolution as the short camera with the 110 l/mm grating, using a comparable slit width in pixels, but with 3x the spatial resolution. Because of the significant slit losses (e.g., a 0.1 arcsec slit is required to match the resolution of the 0.3arcsec slit with the short camera), this mode is only recommended when very high spatial resolution is desired.