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31.6 Recalibrating FOS Data: A Checklist

You will use the IRAF/STSDAS task calfos. to recalibrate your FOS spectra. This task sequentially performs each step described in the preceding section.

Here is a checklist of things that you should routinely do to re-calibrate any FOS exposure:

  1. Add new or updated keywords: The first thing to do is make sure that your data have all the required keywords in their headers. The STSDAS task addnewkeys will update the headers of your .d0h files accordingly. This task insures that the AIS flux calibration method keywords are in the header and also adds the scattered light correction keyword to older pre-COSTAR files. Note that a default set of reference filenames is used for the new calibration switch keywords - you must update these as part of the next point on this checklist.
  2. Get correct reference file names: Next you must determine which are the correct reference files to use. You can determine the correct reference files and tables to use for re-calibration of any exposure by using the StarView FOS calibration reference file screen (see section 1.3 for a complete description of this procedure). Alternatively, the FOS WWW Reference File Guides provide a listing of recommended FOS reference files as a function of observing epoch for each type of reference file or table.
  3. Update header files: In order to recalibrate FOS data using updated calibration files, you need to edit the header of the original science data, .d0h, with the task chcalpar and replace the names of the original calibration files with those of the new ones. If required, you should also update the values of YSTEPn for paired aperture exposures as described in section 31.5
  4. Set DEFDDTBL to "F" (false): As noted earlier, some header files may have had the Default Dead Diode Table keyword set to TRUE in order to use the .udl file to specify the list of dead diodes for original pipeline processing. Since a complete history of dead diode occurrence dates is now available, only the DDTHFILE should now be used to identify dead diodes. Under no circumstances should DEFDDTBL be set to "T". Naturally, it is also a good idea to make sure that all other calibration switches are set properly at this point.
  5. Run the calfos calibration routine: calfos will create new calibrated output files with the same suffixes as the originally delivered data, namely .cnh and .cnd (n=0...8).

If you are concerned about any aspect of the appearance of your calibrated data, you should compare the final data with flatfield (and other) reference files used in the data reduction process to make sure that spurious features were not introduced through improper data handling in the pipeline or in your recalibration.



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