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Calibrations for GNIRS consist of the following measurements.
- Observations of telluric standard stars to correct for telluric absorption. For guidance on standard star exposure times see here. Note that often accurate airmass matching is critical.
- Flat field spectra.
- Spectra of one or more arc lamps for wavelength calibration in the 0.9-2.5 µm region (at 3-5 µm the telluric lines in the spectrum of the science target or calibration star provide wavelength calibration).
- Pinhole observations to trace the spectrum on the array; usually needed only for cross dispersed data.
All calibrations, including tellurics, flatfields and arcs, must be specified in the Phase II definition. These "baseline" calibrations are summarized in the context of all Gemini Near-IR instrument calibrations (i.e. 1-5 µm imaging and spectroscopy).
Flat-fielding and arc lamp wavelength calibrations for GNIRS are obtained with the facility calibration unit, GCAL. Flats and arcs are obtained at night near-simultaneously with science observations. Pinhole calibrations are carried out during morning or evening twilight or in daytime.
Further information on near-IR calibration, including line lists, standard star search tools and spectral template libraries, can be found on the NIR resources pages.