Sensitivity

Sensitivity degradation is typically less than 2% per year, as seen in plots of sensitivity vs. time for the G140L, G230L and G750L gratings. This time dependence is now incorporated in the STScI data-reduction pipeline for all STIS first-order configurations: it was implemented in 2002-May for the MAMAs (see ISR 2001-01) and in 2003-Nov-13 for the CCD.

New trends in the sensitivity degradation have been observed in the last two years and were incorporated in the pipeline on 2004-Apr-16.

STIS sensitivity can be evaluated interactively using the web-based Exposure Time Calculators (ETCs).

Count rates can also be determined manually from sensitivities, using definitions and formulae in the STIS Instrument Handbook.

Sensitivity may also be characterized in terms of limiting magnitudes for spectroscopic and imaging modes. These tables list V magnitudes that yield S/N=10 for an A0V stellar input spectrum.