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Baseline Calibrations

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Baseline calibrations include:

  • Biases
  • GCAL flat field
  • GCAL ThAr arc
  • Flux standard star 

The day before GRACES is schedule for the night, a series of flats, arcs and biases are taken for each read mode and spectroscopic mode. Those baseline calibrations are shared by all programs observed in that same night. Spectrophotometric standards are observed each semester in both spectroscopic mode during poor weather nights. They can be used for flux calibration for all the science spectra observed during the semester.

Applicants should not include time for baseline calibrations in their Phase I proposals. 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. Any time required for additional calibrations between the hours of nautical sunset and sunrise to obtain baseline calibrations will be charged to that particular program.


Measurement Type Notes
Bias A series of biases in all read modes are obtained daily.
GCAL flat field Flat fied calibration frames are obtained as part of daytime baseline calibration using light sent through the fibers from GCAL to ESPaDOnS. A total of 20 frames are observed per day, per spectroscopic mode, per read mode, to ensure the extrction is not limited by the flat field signal-to-noise ratio.
Wavelength calibration

ThAr exposures for each spectroscipic mode are obtained as part of daytime baseline calibration.

Flux standard stars

Selected from the sources listed on the GMOS spectrophotometric standard star page. One spectrum per spectroscopic mode is observed each time GRACES is installed. Observations are not guaranteed to be obtained during the same nights as the science observations for the program. Observations to provide absolute spectrophotometric calibration are not included as part of the baseline calibration set.

Telluric standard star The flux standard stars may be use for approximate removal of telluric lines but the observations of the flux standard are not guaranteed to be obtained during the same nights as the science observations for the program.
Radial velocity standard star Radial velocity standards are not observed routinely as part of baseline calibrations. Any program that requires radial velocity standards should include these observations in the phase II for the program.
Darks The ESPaSOnS dark current is 0.0126 é/pix/h. Dark images are not taken.
Bad pixel mask A bad pixel mask is produced by the extraction pipeline OPERA. 

Gemini Observatory Participants