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ALFOSC flat field images

Master flats are created as a last command in alfosc.easyflat, if three or more twilight flats are available. The script will check the average counts of the full frame are between 69.999 and 319.999 ADUs. First the overscan ([2104:2146,*]) is subtracted and then all the frames are trimmed ([51:2098,2:2041]) using iraf/mscred/ccdred-task. For the time being these two sections are "hard coded" as the proper keywords are not available from the FITS headers. The processed images are combined using iraf/mscred/flatcombine.

The output file-names have a format like "ALyg13_109_flat1.fits", where "ALxxyy" is the normal prefix, followed by the filter id and the "flat1" indicates that this was the first "flat" for the filter of the night. If the easyflat-script is run again the number will increment. e.g. "ALza25_12_flat2.fits".

The masterflats are available from the ALFOSC master-flat ftp archive .

The iraf commands for creating the master flats are like:
>ccdpr AL*s oversc+ trim+ trimsec=[51:2098,2:2041] biassec=[2104:2146,*]
>flatc AL*s out=ALyg13_109_flat1

Some old obsolete dome flat stuff here

Back to top Last modified: April 19 2023