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The software available in the CCD package takes care of the relative calibrations of the pixel intensities, of averaging, and of cleaning frames. Cleaning in this context means removal of the instrumental signature and other defects from the frames.
A full reduction of CCD data involves the steps outlined below:
Some of these steps are optional and depend on the kind of data you have taken. In addition to the operations described here, MIDAS contains a number of other operations like removing of cosmic rays. As indicated above, all steps can be executed in an automatic (batch) mode provided the keyword settings have been done correctly.
In the automatic procedure, the highest level of processing is the loop over all science frames selected in the Association Table. If, for whatever reason, the processing of a frame fails, this frame is skipped and the processing is continued with the next one.
The CCD package system provides a single command for doing the entire calibration of the CCD frames: REDUCE/CCD. The command is a composition of a number of lower level procedures, each of them taking care of a particular part of the calibration procedure, and executable via a separate MIDAS command. These components are: overscan correction, trimming, combining, bias correction, dark subtraction, flat fielding, illumination correction, and fringe correction.
Whether you want one or more calibration steps be executed depends
on the settings for the various options. Therefore, before starting
be sure that the keywords for the reduction are set correctly. These
keywords and their meaning are listed in
Table . Also, the keywords for combining
calibration frames should be checked. Furthermore, fill the keyword
CCDASSOC with the name of the Association Table, and check that
this table is correct. All keywords can be filled and displayed with
the commands SET/CCD and SHOW/CCD.
Table: Keywords for setting the reduction process