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Flat Field Info

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The baseline default GNIRS flat fields that are obtained near-simultaneously with the science spectra are designed to provide higher signal-to-noise ratio (SNR) flat fields than the SNRs of typical science spectra, in modest amounts of time (a few minutes at most). They consist of a small number of individual flat field frames, which are summed by the user.

For long-slit single order spectra the final (summed) flat fields have SNRs of 200-400 rms, where the range in values roughly accounts for wavelength-dependent filter transmission and grating efficiency.

In cross-dispersed mode the rms SNRs of the summed flat fields are as follows.

  • K (order 3): 200-400
  • H (order 4): 300-600
  • J (order 5): 300-600
  • X (order 6): 200-400
  • 0.95µm (order 7): 150-300
  • 0.85µm (order 8): 70-140
  • orders 9-11: 20 or less

Users who require higher SNR flats than those described above should make their needs known to their NGOs, who can query the Gemini staff contact scientist if necessary.

Gemini Observatory Participants