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Space Telescope Imaging Spectrograph
STAN - March 2001

| HST Spectroscopy                      STIS/GHRS/FOS |
| STScI Analysis Newsletter                  Mar 2001 |
|                                                     |

Errors in Processed TIME-TAG Data from STIS.


Errors in Processed TIME-TAG Data from STIS.

We have identified errors in some processed TIME-TAG 
datasets. These errors will be corrected when raw 
TIME-TAG data are reprocessed by new ground software, 
scheduled for installation in the archive pipeline at 
the end of June. We will make another announcement when
corrected datasets may be retrieved from the archive. 
STIS MAMA detector electronics occasionally report an 
erroneous time. Existing ground processing software 
fails to trap certain newly characterized errors in 
reported time. As a result, gaps or jumps in time may 
occur in processed TIME-TAG data. Also, existing ground 
software does not properly flux calibrate data from 
observations in which the actual exposure time differs 
from the EXPTIME keyword value (i.e. the requested 
exposure time). This can happen when STIS memory fills
before it can be dumped, for example. None of these 
issues affect STIS MAMA data obtained in ACCUM mode. 
All investigators working with STIS TIME-TAG data 
should read the more detailed discussion of possible 
problems at the URL given above. This web page also 
serves as a distribution point for new software to '
detect errors in existing TIME-TAG event lists (_tag 
files), determine apparent exposure times from the 
event list, and correct fluxes in extracted spectra 
(_x1d and _x2d files).

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