When a STIS exposure is interrupted (i.e. for a guide star loss of lock), the take data flag (TDF) goes down, which prevents STIS from obtaining data. If the interrupt condition is relieved (i.e. if guide stars lock is re-achieved), the TDF goes back up and data-taking is resumed. For all data obtained to date, the exposure time keyword in the data header was not updated for possible interruptions, resulting in improper flux calibration of the data; an observation was interrupted if the EXPFLAG keyword in the extension header is INTERRUPTED.

A procedure to correct the exposure time keyword (EXPTIME) has been developed, and will shortly be installed in the processing pipeline. For data already obtained, an IRAF script is available to determine the corrected exposure time and update the EXPTIME keyword. Observers will then need to reprocess their data through CALSTIS to obtain the proper flux calibration.