The gain-sag table reference file (GSAGTAB) has been implemented in the OTFR pipeline as of May 24, 2013. This table identifies regions on the FUV detectors that have been affected by gain-sag and allows for their removal from final calibrated spectra. Users with data taken after August 23, 2010 and before the start of observations at the 2nd FUV lifetime position on July 23, 2012 are strongly encouraged to re-retrieve their observations from the HST archive. Without the GSAGTAB, affected regions may appear similar to absorption features of varying strength, and will need to be removed manually post calibration.
From now on, regular monitoring will identify sagged regions and deliver a new GSAGTAB reference file, if needed, on a monthly basis. Gain-sag features develop slowly, so this delay is unlikely to result in any significant effect on extracted spectra, but users are still encouraged to re-retrieve data after the next monthly update to the GSAGTAB to ensure the best calibration. Gain sag at the second lifetime position has been modest to date and as a result the GSAGTAB should not require frequent updates over the next several months. A future STAN will be used to notify the community when gain sag at the 2nd lifetime position begins to require more frequent updates of this file.