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Wavelength and flatfield calibration (baseline calibrations) are obtained using the facility calibration unit, GCAL in standard and high resolution mode. Baseline calibrations will be obtained for all observations, queue and classical. Additional calibrations (spectrophotometric standards, radial velocity standards, telluric standards, or night time wavelength calibrations) must be requested as part of your program.

Baseline calibrations

For all observations a set of standard, baseline calibrations, shown in the tables below, will be taken by Gemini Staff to ensure the long-term utility of data in the archive. Baseline calibration data may be shared between programs and will be distributed to the users as part of their dataset.

If additional calibrations are deemed necessary by applicants, for example to achieve a precision beyond that achievable via the baseline set, then these must be included explicitly as part of the Phase I proposal and Phase II science program, as program calibrations. All calibration data are available through the Gemini Observatory Archive.

Baseline calibrations
Measurement Type Notes
Bias levels Bias images are taken during the day in all read modes, and binnings for which data are taken.
Flat field corrections Dome flats are taken in the respective resolution and read modes of science, and calibrations during the day using a 100W lamp. All dome flat-field observations are taken in dual target mode, with the two IFUs illuminated evenly. The flats are binned to match the science binning during data reduction.
Wavelength calibration Wavelength calibration is conducted using arc exposures taken during the day with a ThAr lamp in the respective resolution and read modes to match science. There is minimal flexure in the Cassegrain unit, and no nighttime arcs images are taken. All arc lamp images are taken in dual target mode, with the two IFUs illuminated evenly. Arcs are binned to match the science binning during data reduction. 

Program calibrations
Measurement Type Notes
Nighttime wavelength calibrations Arc images can be taken during the night immediately before or after science observations, to match better the ambient conditions of science data. These are taken using the ThAr lamp situated in GCAL, but at the same position as the science target. The data reduction pipeline is only able to process arcs taken with the two IFUs illuminated evenly, unbinned in a read and resolution mode matching the science, and by default arcs will be taken in this configuration. Such observations, if desired by the PI must be requested during Phase I.
Radial velocity standards Radial velocity standards if required for science, must be included in the Phase I time request. Such observations can be taken before or after science.
Telluric standards Wavelength longward of 700nm are contaminated by telluric lines. If your science region of interest requires accurate telluric subtraction, please include a telluric standard closely matching the airmass of your target, so that it can be scheduled before or after the science observation in your time request. An appropriate standard may be found here
Spectrophotometric standards Given the aperture limit and the fiber relay, absolute spectrophotometric calibration is not always possible unless taken in seeing limited photometric conditions. Although spectrophotometric standards are taken as part of the regular instrument monitoring program, these observations are not guaranteed to be obtained during the same nights as the science observations for the program (or in the same instrument configuration). If absolute flux calibration is required for science, please include a spectrophotometric standard in your Phase I time request, which will be charged to the nighttime program calibration. This will be taken in conjunction with your science.

Instrument monitoring program

To monitor instrument performance the instrument team regularly observes nighttime and daytime calibrations. These are not included as part of science calibrations, but are mentioned here for users benefit. 

  • Spectrophotometric calibrations

    • During queue operations, spectrophotometric standard stars for performance monitoring are chosen from the sources listed in the following table, and include the HST white dwarf primary standards, and Hamuy standards. Observations of such standards are usually conducted at both resolution modes every few weeks (depending on queue pressure and observing conditions) in photometric skies and good seeing to monitor instrument throughput. 
Spectrophotometric standard stars
Reference Coverage
Hamuy et al. (1994, PASP, 106, 566) -68 deg to +11 deg 330-1030 nm 5 nm
Bohlin et al. (1995, AJ, 110, 1316) +15 deg to +52 deg 100-30000 nm 0.06 nm

  • Radial velocity standards

    • Beginning during queue operations, regular radial velocity observations of known radial velocity standards are planned to be taken in both resolution modes (and including the PRV mode) to monitor radial velocity stability in a variety of ambient conditions and over time. 
  • Darks

    • To monitor the background current, the instrument team obtain 2 hour long dark exposures every 1-2 months of both science detectors, and shorter dark exposures of the slit viewing camera. These are taken to monitor the dark current of the instrument. Special attention is paid during the Chilean summer, where the instrument shows a slight temperature increase with the increase of ambient temperature at the summit.