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XMM-Newton Science Analysis System


omichain (omichain-1.50) [xmmsas_20070708_1801-7.1.0]

Meta Index / Home Page / OPERATION

Processing of the data for each filter

The omichain then cycles through each filter in the filter list and processes each exposures in the exposure list for that filter. The following summarizes the steps taken by the omichain in this stage.

1. First it checks to see if the exposure is a full-frame low resolution mode, and if so it runs omcomb to combine the four separate image segments into a single full-frame image, which is then processed instead of the individual image segments.

   The tracking-history pipeline is run to produce tracking history information using omprep, omdrifthist and omthconv.

   The imaging pipeline is then run to reduce the image for each exposure, and the following programs are executed in turn:

   1. omprep - converts the image from integer to real and adds some key-words to the header. omcosflag - adds the quality array to the image.
   2. omflatfield - flatfields the image.
   3. ommodmap - attempts to correct for mod-8 patterning.
   4. omdetect - detects sources, computes source positions, source moments (semi-major, minor and position angle), raw and corrected count rates, and sets some flags for each source.
   5. ommag - computes instrumental magnitudes for each source.
   6. omatt. - computes celestial coordinates (Right-Ascension and declination) from the X and Y pixel coordinates and produces a ``sky-image''. If a USNO catalogue fits file is available, and the parameter usecat is set to true then it will also correct the astrometry for any offset between the OM and USNO RA and dec axes, adding the columns RA_CORR and DEC_CORR to the source-list.