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: http://www.stsci.edu/documents/dhb/web/c26_stisdataanal.fm4.html
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Note that the times given in the first column of the raw time-tag data (which is the time relative to the start of the exposure) are not corrected for the time delay due to the motion of the earth or the spacecraft. The change in time delay due to the motion of the spacecraft can be a maximum of about 30 millisec in one orbit. The absolute time delay relative to the time-frame at the earth barycenter can itself be much larger. To correct for these effects, the ephemeris of the earth and the spacecraft are necessary. A separate task is being developed at present, similar to the tasks for the High Speed Photometer (HSP), to correct for these effects and to convert the times to the barycenter of the earth. This task can be used by observers, or can be processed at STScI as a special request, for those science uses of TIME-TAG where it becomes an important effect.
Using inttag to Produce ACCUM Images of Specified Time Slices
The inttag task can be used to integrate STIS timetag data into an image or set of images. The default behavior for inttag is to accumulate all events from the table, writing the results as one image set in the output FITS file. The user has the option, however, to specify explicitly a starting time, time interval, and number of intervals over which to integrate, in which case a collection of image sets will be written to the output file, simulating a REPEATOBS ACCUM observation. Breaking the data into multiple, short exposures can be useful not only for variable targets but also to improve the flatfielding when the Doppler shift is significant.
cl> inttag stis_tag.fits kilo_raw.fits sttime=0 increm=1000A somewhat more complex example is to create 20 high-res imsets, each 100 seconds in duration, starting at the first time in the GTI table. Note that while 20 imsets were specified, fewer may actually be written if any of the 100-second intervals is not contained within any GTI, or if the last time in the GTI table is less than 2000 (i.e. 100 sec * 20 intervals); inttag will report how many imsets were created.
cl> inttag stis_tag.fits multi_raw.fits sttime=0 \
>>> increm=100 rcount=20 high+Once the images have been created, it is straightforward to process them with calstis and analyze the output images or spectra, as appropriate (see "Recalibration of STIS Data" on page 21-29).