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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 0.3-5 um 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

March 2005: Krypton lamp replaced with Xenon for higher line density

Pervious versions: October 08 2007 by Rachel Mason. Original pages by Bernadette Rodgers and Phil Puxley