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GCAL
A Gemini Facility Calibration Unit (GCAL) is available on each Gemini telescope, providing continuum and line emission light sources for wavelength and flat-field calibrations. Each GCAL is located permanently on one port of the instrument support structure and light is directed into an instrument by the science fold mirror. The GCAL optics simulate the f/16 telescope beam, illuminating the instrument pupil in the same way as light from an astronomical source. Instruments within the wavelength range 0.3-5um can be calibrated; mid-IR instruments are calibrated by other means.
GCAL is operated via flat and arc observations defined in the OT as part of each program's Phase II definition. Proper selection of lamps, ND filters and exposure times depends on the instrument being used and more information is available on the individual instrument web pages. The available line and continuum calibration lamps are shown in the table below.
| Lamp Name | Typical Usage | Example Spectra |
| Arc Line Lamps | ||
| Argon | Near-IR spectra | GNIRS and NIRI spectra and line IDs |
| Xenon | Near-IR spectra | GNIRS spectra and line IDs |
| ThAr | High-res optical spectra | |
| CuAr | Optical spectra | GMOS spectra and line IDs |
| Continuum Lamps | ||
| Quartz halogen | Optical/Near-IR flat fields | |
| Grey body (1100K) | Near-IR flat fields | |
Notes:
March 2005: Krypton lamp replaced with Xenon for higher line density
Last update October 08 2007 by Rachel Mason; original pages by Bernadette Rodgers and Phil Puxley