omdetect (step8). The task omdetect applies a source
detection algorithm to find the sources present in the image. First the
background is modelled. Then the algorithm looks for sources matching the
criteria defined by the task parameters. Aperture photometry is applied to
the detected sources. The point spread function (PSF) of OM is taken into
The output is a source list (SWSRLI) which contains the source positions
in absolute detector pixel and the calculated sources and background
count rates (cts/sec). Coincidence loss correction is also applied to the
count rates of the sources and the background.
An optional output file, called the region file, can be generated with a
name defined by the parameter regionfile. The region file describes the
area associated with each identified source in the image. It is used by the
image display tool.
Extended sources are also identified if the parameter detectextended is
set. The photometry of an extended source is made by adding all the counts
received in an elliptical area and the background is measured in an annulus,
as for point sources. Coincidence loss correction is applied by considering
that every pixel is a point like source.
Since SAS v9.0, omdetect can be used on final mosaiced or stacked images
in order to find fainter, previously undetected sources.