XMM-Newton Science Analysis System


omdetect (omdetect-5.0.7) [xmmsas_20050815_1803-6.5.0]

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Algorithm

subroutine omdetect

read data for selected OSW image 

get mode of image by sigma clipping to get average 
background level
Loop though all pixels on the image- for each pixel with a value >=nsigma *
background mode analyse surrounding pixels to ascertain if these pixels may 
constitute a ``point'' source. If so, set the pixels to an assigned source
number, compute the source position and shape by moments, and store the
parameters. Repeat until all pixels have been checked.



Recompute the background mode, ignoring those pixels assigned to a point-source.
Check all the remaining pixels and those with a value >=nsigma *
background mode assign a number. Analyse these pixels for individual extended
sources and  assign a number to each one. Compute the source position and shapes of
each extended source by moments, and store the parameters. 


Perform aperture photometry on each source.
Examine each point-source and discard any with a significance less than the
minimum allowed value.

Examine each extended source to attempt to see if it is just scattered light
around a point-source- reject this source if it is.
  
write output sourcelist containing source parameters. Also output 
detection count rate threshold. 


end subroutine  omdetect