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FORS1 Quality Control:
Detector Parameters

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   gain & linearity
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conversion factor
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This page refers to the determination of linearity and gain by the DETMON recipe. Data derived traditionally from imaging screen flats by the fors pipeline can be found here.

top Detector Parameters

To measure the detector parameters a sequence of imaging screen flat field pairs is observed in the R_BESS filter and for the standard readout modes (100Kps/high_gain/2x2 and 200Kps/low_gain/2x2). An appropriate set of bias frames is included in the template.

QC1 parameters

  • conversion factor (gain) (QC1 database table fors1_detmon, column gain)
    For every pair of flat fields with identical exposure times the difference of the average of the bias-corrected frames is compared to the difference in rms between the bias and the flat field difference. This comparison is limited to the illuminated parts of the CCDs. The factor relating the two quantities is the gain in e-/ADU. For method=PTC (Photon Tranfer Curve) a linear relation is fit to these quantities for the various exposure times.
  • linearity coefficients (QC1 database table fors1_detmon, columns lin_coefi, lin_coefi_err with i=0,1,2)
    For each exposure time the mean and the median of the bias-corrected flat fields (restricted to the illuminated area of the CCDs) is calculated. Then a second order polynomial is fit to the mean/median vs. the exposure time and the coefficients of that polynomial are stored in the columns mentioned above. In general the contant and the second order terme are 0 within their errors.
  • effective non-linearity (QC1 database table fors1_detmon, column non_linear)
    The effective non-lienarity is the difference between the polynomial flux and the one predicted by the linear fir at user-defined flux level (column flux_non_linear), normalized with the polynomial flux.