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Robert Armstrong, 07/30/2012 09:17 AM


Cal-R1

A photometric model (i.e. flat fields and sky-­‐subtraction methodology) is in place which produces relative magnitudes between bright stars that are reproducible to <0.02 mag RMS on different exposures taken (a) at different times during a cloudless night (b) on different cloudless nights up to 3 weeks apart. [This is essentially a test of whether we can construct a flat field that describes system response to light and remains stable. DECAM TG-­‐12. DECam TO-­‐8 covers pupil ghosts, TD-­‐10 is QE gradients]

Prerequisites

  • Observation of rich stellar density field during photometric conditions for model construction. Dither pattern?
  • Use overlapping DES survey data to test model. Need repeated observations separated by 3 weeks.
  • Need single epoch catalogs with astrometric solution <1"

Procedure

  • During Commissioning
    • Use observation of dithered, dense stellar field to derive large scale variations of the stellar photometric response
  • During Science Verification
    • Test model on DES survey data with repeated observations on same night.

Verdict

  • Relative photometry of bright stars < 0.02 mag RMS

Consequences

If the requirement is not met we may need to refine model or reexamine flat-fielding and sky subtraction methods.