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*imcnts* - Use of the Sky Coordinate System

The following example reproduces that in *imcnts* - Find background subtracted counts for a point source, but using celestial coordinates sky (world), and using different size source and background regions.

input file: xdata$rp110590.qp

output file:

  xr> xspatial                                          # Load the spatial package 
  xs> imcnts                                       # Run the task to count photons 
  source image file :  xdata$rp110590.qp                              # Input file 
  source region descriptor :  c 22:08:41.6 45:45:04.7 3'
                               # Circle at RA=22h 08m 41.6s, Dec 45 deg 45' 04.7'' 
                                                         # with radius of 3 arcmin 
  background image file or cts/pixel: xdata$rp110590.qp       # From the same file 
  bkgd region descriptor:   a 22:08:41.6 45:45:04.7 3.3' 4.4'            # Annulus 
                     # of 3.3 to 4.4 arcmin radii, centered at the source position 
  root name for output file []:  rps90    # Output table

It is also possible to combine pixel and sky coordinates. For example c 232 313 2$^{\prime}$ is equivalent to c 232 313 240 for the ROSAT PSPC (0.5 $^{\prime\prime}$ per pixel).