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Exposure Time Estimation

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Exposure times

The numbers in the table represents the suggested exposure times for the various metamodes for a given magnitude in the science band. The given exposure time is set so that the counts are well in the linear regime. The PI should be aware that we don't recommend exposure times significantly longer than 60 seconds as the sky rotation may smear the putative planet. It should be noted that the exposure times are in multiples of 1.45479s with the final exposuretime in GPI is rounded down to be a multiple of 1.45479s. 

max exposure time=10((magnitude + 0.845 + MODE )/2.5)-1.5

where magnitude is the magnitude in the science band of the central star, and, MODE has the following values pending the meta mode:

  • Coronography Spectroscopy: MODE=0.0
  • Coronography Polarization: MODE=-2.0
  • NRM Spectroscopy: MODE=-3.0
  • NRM Polarization: MODE=-4.5
  • Direct Spectroscopy: MODE=-7.0
  • Direct Polarization: MODE=-9.0

These exposure times will fill the detector to the 1% non-linearity level and there is a small margin of ~10% in counts to significant non-linearity.

N.BThe above formula is based on ONLY halo light from the central star. Any companion should use the DIRECT mode correction for any calculation.