Interactive OM image data reduction with SAS

This thread helps you to run SAS task omsource and perform interactive photometry with OM. This is a step-by-step recipe, for all details please read SAS manual.

1)  Set things up:
    
    a) Before you can run task omsource properly, the environment variable for 
       running SAS must be set. Please read SAS start-up thread at: 
       http://xmm.vilspa.esa.es/external/xmm_sw_cal/sas_frame.shtml. If you 
       can run OM pipeline chains 'omichain' or 'omfchain', that means that 
       the environment variable has been set.
        

    b) The task omsource works on SAS processed image (after flatfield and 
        mod8 corrections). This image file is included in the PPS product, and 
        has file name PxxxxxxxxxxOMS*IMAG_*000.FIT (for example, 
          P0158360201OMS012FIMAG_U000.FIT, corresponding to a full frame low 
          resolution image)     




2)  start by typing the following command and pressing return -

   omsource imageset=P0158360201OMS012FIMAG_U000.FIT newsrclistset=slist.fit

    where:

         'imageset' uses the image file PxxxxxxxxxxOMS*IMAG_X000.FIT in the 
           PPS product.    

         'newsrclistset' is a new source-list file with an identical 
           structure to that produced by the SAS task omatt, therefore 
           it can be used as input file to the SAS task omsourcelistcomb.
   You can also add another parameter 'oldsrclistset', using an existing 
   source-list file (for example, PXXXXXXXXXXOMSXXXSWSRLI*.FIT from PPS). 
   The source stored in this source-list file are numbered in the image. This 
   is useful to check the results from the PPS.           


   The parameters 'imageset' and 'newsrclistset'  are mandatory for SAS 5.4.1 
   or before, they can be omitted for a later SAS version (SAS 6.0).
  
3) select sources 

    After typing the command in step 2), the main task window and the image 
    will be displayed as below.     

 


 

    From the main task window, you have only two options ('Add sources' 
    and 'Run omdetect'), either select sources from the image manually, or 
    run the SAS task omdetect to locate sources on the image, by clicking 
    the appropriate button.

   a) select sources from the image manually (if you are interested only 
       on the main target or few sources on the image ) 

   -- clicking the button 'add source', the task window is hidden and a small 
       window appears as this Figure.

    
  
   -- You can select additional sources in the image by centering the cursor 
      over the source and clicking the mouse button. 
   -- When finished, press the 'Finished' button in the small window.  
   -- The main window is shown again. The region for each source is displayed 
      on the image as a yellow ellipse, and the top list box is loaded with 
      parameters (RA, Dec, corrected count rates, instrumental mag) of each 
      source.  
  
  or   

   b) run omdetect automatically (if you are interested in all sources on the 
        image)
   
   -- Click the 'Run omdetect' button, a small dialog-box is displayed allowing
       you to change the parameters nsigma, minsignificance and detectextended.
 
  
    


   -- The sources will be selected automatically when clicking 'OK' button in 
      the small dialog-box. 
   -- Each detected source is displayed on the image as a yellow ellipse and 
      the top list box is loaded with the parameters of each source. 
   -- Check the detected sources on the image, if the results are not 
      satisfactory, click the  'delete list' button in the main window and 
      then click the 'Run omdectect' again by changing the detecting parameters
      until the results are satisfying.  
 

 4) redo photometry for selected source 

   a) the  source has first to be selected 

  -- In the Source selection control group click on the spin-box control to 
     either increase or decrease the source-number. When the required source 
     number (834 in following Figure ) is shown click the select button. 
  



 
  b) Having selected the source, the source is then displayed by ds9 
    (see Figure 5). The region is displayed by a yellow ellipse and the 
     photometry aperture, the inner and outer background radii, are indicated 
     by blue circles. 
Figure 5



                                                                                                                              
  c)  Change the aperture radius and background annulus  by clicking on the 
       appropriate spin-box control. When the 'apply' button is clicked the 
       photometry is recomputed using the selected aperture radius and 
       background annulus. 

  d)  You can repeat step c) above by changing the aperture radius and 
      background annulus. Each time the 'apply' button is clicked, the
      recomputed photometry parameters for the selected source, including 
      the original value is stored in the 'logger table' in the lower part 
      of the main task window.  An average magnitude is computed from all the 
      entries in the logger table and printed in the average magnitude table 
      just below the logger table.