QC1 parameters

• effective non-linearity (QC1 database table hawki_detlin, column qc_lin_eff, product keyword QC.LIN.EFF)
  

  The effective non-linearity is the difference between the polynomial flux and the one predicted by the linear fit at user-defined flux level, normalized with the polynomial flux.

• conversion factor: conad/gain [ ADU/e- ] (QC1 database table hawki_detlin, column qc_conad, product keyword QC.CONAD)
  

  For every pair of ON frames obtained with identical DET.DIT (in Ks filter using the Nasmyth shutter as a source), the difference of the average of the OFF-corrected frames is compared to the difference in rms between the OFF and the ON frames. The factor relating the two quantities is conad in ADU/e- or gain in e-/ADU. For method=PTC (Photon Tranfer Curve) a linear relation is fit to these quantities for the various DET.DITs.

  2016-08-30: It was noticed by Alain Smette that the template delivering the data uses NDSAMPLES (the number of times the detector is read within a DIT) and NDITs that are different depending on the DIT. The higher DIT, i.e. the higher flux, the higher NDSAMPLES. As the relation of the variance of a frame with the intensity depends on NDSAMPLES and NDIT, the gain determination is incorrect. It can still be monitored for trending purpose though. Further work on template and/or pipeline recipe design is to follow. In the meantime (starting from data on 2016-04-27), the recipe (detmon_ir_lg) parameters were set to exclude high flux frames from gain determination:

  • --filter=2500 (following the detector DET.SETLEVEL parameter)
  • --gain_threshold=1500