.help exomerge sep98 ftools.exomerge
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NAME
exomerge -- merge compatible EXOSAT LE event files
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USAGE
exomerge @evtlist outfile
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DESCRIPTION
   This task merges event files obtained from a single observation with the 
   EXOSAT CMA detector and it corrects the reference coordinates if 
   data were taken with the star tracking mode STR1.
   It is intended to work for EXOSAT CMA raw data files as stored in the 
   HEASARC archive. The content for each observation includes a catalog file,
   an orbit file and several event and housekeeing files. Within an 
   observation, a new event and housekeeping file was created either after a
   few hours of observing time (ranging between 2-4 hr) or because of changes 
   in one or more observational parameters. 
   The task checks that all the input event files share the following modal 
   parameters: pointing mode (STAR_PNT), detector (INSTRUMENT), energy filter 
   (FILTER), on board computer mode (OBCMODE), and the same grating setting 
   (GRATING). An error is reported for any of the above modal parameter 
   differences found. The task will stop execution and no merged file is 
   created. Before restarting the process discard in the list of input event
   files those with different modal parameters. 
   A warning instead is given, if the data were taken with different background
   filters, known as the diamond filter. This filter masks part of the 
   detector FOV. The merged event file is created but it is usable only 
   within the diamond region (e.g. outside the exposure will be 
   underestimated). 
   The 'exomerge' output file will have all the extensions merged, the data 
   sorted in time and the timing header keywords updated. 

   EXOSAT could be programmed to maintain the spacecraft attitude in two
   modes, start tracking mode 1 (STR1) and 2 (STR2). In STR1 the spacecraft 
   attitude was maintained using one star in the star tracker field of
   view (FOV) and the position of the sun determined using the fine sun 
   sensor (FSS). STR2 instead used two stars in the star tracker FOV. 
   In STR1 mode a correction to the reference coordinates is needed to 
   account for the roll error in the spacecraft attitude. The correction 
   modifies the RA_NOM, DEC_NOM, TCRVL2, TCRVL3, TROTA3 and TCROT3 keywords 
   in the merged event file. This is calculated using routines from the 
   EXOSAT Interactive Analysis software package and the information stored 
   in the housekeeping and orbit files. The calculation uses the housekeeping 
   values corresponding to the midpoint of the time interval between the first
   and the last input event file. A warning is given if there are no 
   housekeeping data available at the midpoint observation time (e.g. for a 
   data gap). In this case the correction is based on the housekeeping values 
   at the closer midpoint time.

   Exomerge can be run standalone or using two different scripts
   which create the input list for exomerge and run exomerge.
   The first, tkexomerge, is a graphic user interface using Tcl/TK
   which displays the content of the catalog file and allows the user 
   to create the input list by mouse selecting the event files to merge. 
   The other, automerge, is a perl script which creates a list of event files
   on the user response to a few input paramaters (e.g.detector, filter type, 
   and the grating setting).

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PARAMETERS
.ls evtfile [string]
Filename of the ASCII file containing the list of event files to be merged.
.le
.ls outfile [string]
Output filename for the the merged event file.
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.ls tchat (terminal chattiness) [integer]
Set terminal chattiness. 
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.ls lchat (log file chattiness) [integer]
Set log file and chattiness in the log file: = 0 the log file is 
not written.
.ls clobber (overwrite output file if it exists?) [yes/no]
Allows or prevents output file from being overwritten.
.le
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EXAMPLES
.nf
    Create a merged event file, out.evt, using the event files listed in the 
    file evtlist.

   > exomerge evtfile=@evtlist outfile=out.evt 
.fi
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SEE ALSO
tkexomerge, automerge
