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Flat Field Info

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.