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Space Telescope Imaging Spectrograph
New Time-Dependent Sensitivity Corrections

Over the past two years, there has been a significant slow-down of the decline in the time-dependent sensitivity (TDS) of STIS observational modes. New TDSTAB reference files are in the process of being delivered to the pipeline and will correct extracted fluxes for first-order STIS CCD and MAMA spectra for sensitivity changes to a typical accuracy of 1% or better. For recent data, using the new TDS file in place of the previous one will change extracted fluxes by roughly 3-5%.

These new TDS trends will also be incorporated into reference files used by SYNPHOT and the STIS ETCs. This will allow count rate predictions to take the sensitivity changes into account. The default TDS throughputs for SYNPHOT and STIS ETC calculations will assume a date of 2004-Jul-01.

The updated reference files will be installed for use with the ETC by 2004-Apr-16. By the same date, the revised SYNPHOT files should also be available from

Currently the CALSTIS pipeline software applies TDS corrections only to 1D extracted fluxes for first-order MAMA and CCD spectra. SYNPHOT and the ETC also apply TDS corrections to MAMA and CCD imaging calculations. We hope to add TDS corrections for echelle modes in the next few months.

The new trends are plotted below (select a plot to see a larger version).