Merging of Source Tables

 

The source tables created by the local (command DETECT/LOCAL) and by the map detection (command DETECT/MAP) can be merged to one merged source table. Merging means to check whether the distance between two sources is less than the sum of the size of the detection windows times the scaling parameter MIN_DIST_CELL or less than the FWHM of the point spread function of the instrument times the scaling parameter MIN_DIST_FWHM. The algorithm to merge the source tables includes the following steps:

1. Read the source tables and sort the sources by decreasing signal-to-noise ratio (read from table column :SIGNA).
2. Compare the sources in the tables and check for identifications.

The command

MERGE/SOURCE_TABLES smpar edit

  works from the parameter file smpar.par (cf. Table 5.6). This parameter file can also be created (for the experiment ROSAT PSPC) with the command

  
Table 5.6: Parameter file for MERGE/SOURCE_TABLES for ROSAT PSPC

CREATE/PARFIL EXSM smpar ROSAT,PSPC.

• MISSION,DETECTOR is the experiment identifier. Allowed values are ROSAT,PSPC, ROSAT,HRI, and ROSAT,WFC.
• OBS_MODE is the observation mode. Allowed values are POINTING or SURVEY.  
• NUM_IMAGES is the number of energy bands, the maximum allowed number is 3. Source tables created in these bands have to be given in the parameters LDETECT_LIST_N and MDETECT_LIST_N. N runs from 1 to NUM_IMAGES.
• LDETECT_LIST_N is the name of the N-th source table coming from the local detection (command DETECT/LOCAL). N runs from 1 to NUM_IMAGES.
• MDETECT_LIST_N is the name of the N-th source table coming from the map detection (command DETECT/MAP). N runs from 1 to NUM_IMAGES. In case one wants to merge just two local detection tables LDETECT_LIST_1, one has to set NUM_IMAGES to 1 and MDETECT_LIST_1 to LDETECT_LIST_1. This makes sense, as the same source may have been detected with different compression steps in the local detection. The same procedure applies in case of merging two map detection tables.
• MIN_DIST_IN_FWHM is the minimum allowed distance in units of the FWHM of the point spread function between two sources considered as separate sources. The default value is 1. A value larger than 2 should not be used.
• MIN_DIST_IN_CELL is the minimum allowed distance in units of the detection cell size between two sources considered as separate sources. The default value is 2. A value of 1 is sometimes recommended to be used in case of close pairs of stars (double stars). A value larger than 2 should not   be used. One has to be aware, that the map detection, which is sensitive to   extended structure in an image may create blobs of sources.   These blobs may   end up after the merging process in anything undefined in case the parameters MIN_DIST_IN_FWHM and/or MIN_DIST_IN_CELL were not set properly. If one sets MIN_DIST_IN_FWHM to a value <0.5 and MIN_DIST_IN_CELL to 0., the blob goes to the merged list.
• BG_IMAGE_N is the name of the background image for the N-th energy band. The value of the background counts per image pixel is determined at the merged sources position and written to the table column :BACKG.
• MERGED_LIST is the name of the merged source table which is created. It contains the merged source position and for each merged position all the multiple entries contributing to the merged position. The number of continuation lines is given in the table column :COFL. If one selects the merged source table for values :COFL.GT.0 one ends up with a table containing just the merged source positions.

There is a set of extended parameters which normally does not appear in the parameter file. They are not needed in standard processing. If, however, one of these parameters needs to be set, they can be accessed via WRITE/PARFIL or CREATE/PARFIL with the extended option.

• FULL_OUT_FLAG is a flag controlling the output. If activated, some additional output files for debugging issues are produced.
• FWHM_CAL_FILE is the FWHM calibration table (to be found in the calibration area). Allowed values are EXSAS_CAL:fwrops.tbl (PSPC), fwrohr.tbl (HRI), fwrowf.tbl (WFC), and frwos1.tbl, fwros2.tbl, fwrop1.tbl, fwrop2.tbl (WFC filter-specific tables). This parameter has to be set only if a WFC filter-specific table shall be used.
• BG_SCALE is the scaling factor for the background image. Defaulted to 1.