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D.J. Stys, R. Bohlin, E.T. Smith, N.R. Walborn (STScI)
The sensitivity of STIS first-order CCD and MAMA modes has been monitored for the past two years via observations of standard stars. These observations reveal small but significant changes in sensitivity. The largest changes are in G140L, where the sensitivity varies with both time and temperature. The sensitivity drops by 0.25 increase in temperature. After correcting for temperature, the sensitivity change is of order 1 sensitivity also varies with wavelength from about 1% to nearly 3%/yr. The mean sensitivity of the G230L mode increased by about 2% in the first 1.3 years and then began to drop at a similar rate. The low-dispersion CCD modes did not experience such changes in sensitivity. For G230LB and G750L, most wavelength bins show no change in sensitivity within a three sigma uncertainty. For G430L, the losses in 200 Å\ wavelength bins beyond 3300 Å\ range from 0.5% to 0.7%/yr with high statistical significance.
The author(s) of this abstract have provided an email address for comments about the abstract: stys@stsci.edu