Space Telescope Science Institute
COS Data Handbook 2.00
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COS Data Handbook > Chapter 3: COS Calibration > 3.5 Descriptions of Imaging Calibration Steps

The processing of image data is depicted in Figure 3.5. It is an abbreviated version of the pipeline that only involves those steps which identify bad data and linearize the initial counts. No absolute flux calibration is performed and no background is identified or subtracted.
The final data products for image data are the flt and fltsum files described in Section 2.4.2. Although the data are not calibrated, a crude calibration of imaging data can be performed using the total count rate from the _flt file and one of the two keywords provided in the count rate extension header. The header keyword PHOTFLAM is appropriate for a source spectrum that is flat and featureless across the MAMA detector band when measured in units of power/area/wavelength and PHOTFNU is appropriate for a source that is flat in power/area/Hz units. The values provided for the PHOTFLAM and PHOTFNU keywords depend on the specific combination of mirrors and apertures used in the observation.

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