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FORS2 Pipeline:
Recipe for Spectro-Polarimetric Calibration Data

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  • recipe name: FORS_PMOS_CALIB
  • input frames: SCREEN_FLAT_PMOS+LAMP_PMOS
  • associated templates: FORS2_pmos_cal_daycalib
purpose: Creates all necessary calibration products to process PMOS SCIENCE data

description: This recipe identifies reference lines on PMOS arc lamp exposures, and traces the spectral edges on the associated flat field exposures. With this information the spectral extraction mask to be applied in the scientific data reduction is determined. The recipe takes into account the fact that every slit in the mask produces two slits in the observed frames. From the input flat field exposures a normalised flat field frame is also derived. The input arc lamp and flat field exposures are assumed to be obtained quasi-simultaneously, so that they would be described by exactly the same optical distortions.

products (for naming rules see here):

  • normalized master flat field (MNFP), derived by dividing the master screen flat by its smoothed version
  • master screen flat field (for verification only, MSFP), master screen flat. Comparing it to the normalized master flat allows to see if all slitlets for MOS/MXU have been found.
  • dispersion coefficients table (PWCP) containing the wavelength calibration polynomial coefficients. This table contains as many rows as in the reduced lamp image, ordered in the same way.
  • slit location table (PSLP) containing the slit positions on the CCD, and on the reduced lamp image
  • wavelength map image (PWMP) with the same size as the CCD, where to each pixel is assigned the value of the wavelength at its center
  • spatial map image (PSMP), which has the same size of the CCD, where to each pixel is assigned the value of its distance (in CCD pixels) from the top edge of the spectrum it belongs to. In case of confusion between nearby spectra, the spatial coordinate would just reflect the spectral curvature, and not the absolute spatial coordinate along the slit (see manual for more details).
  • spectral resolution table (PSRP) containing the mean spectral resolution for each reference arc lamp line
  • curvature coefficients table (PCCP) containing the coefficients of the polynomials used to fit the spectral curvature
  • reduced lamp image (for verification only, PRLP), i.e. rectified and wavelength calibrated arc lamp image. This is the result of applying the extraction mask derived from the flat field and arc lamp exposures to the input arc lamp exposure itself. This image is just useful to get an immediate feeling of the goodness of the computed extraction mask.

 
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