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G.L. Mitchell, G.A. Kriss, P. Goudfrooij, K.C. Sahu, R.A. Downes (STScI)
CTE: Results show that after 3 years in orbit, the STIS CCD is now exhibiting measurable losses in Charge Transfer Efficiency (CTE), which can be of the order 20% for signals of 100 e-/pixel at chip center. A calibration program is under way for a quantitative understanding of the decreasing CTE. We will present results from this ongoing calibration program on functional dependencies of the CTE on source intensity, sky background, source extent, and time. The CTE losses can have pronounced effects on spectroscopic observations. Results on the effect of CTE on Spectroscopic quantities such as equivalent width measurements will also be presented, both for absorption lines and emission lines. To mitigate CTE losses in spectroscopic modes, we have defined a set of "pseudo-apertures" that center a target at row 900 of the CCD. This is 5 times closer to the read-out amplifier, and therefore should reduce losses to 5% or less. These apertures would be most appropriate to use for compact objects with spatial extents less than a few arcseconds, such as galactic nuclei.
MAMA LSFs: The high-resolution Echelle modes of STIS need special care in generating the line spread functions (LSFs). A calibration program using external targets was undertaken to create the LSFs for these high-resolution modes, the results of which will be presented.
OTFR: Starting this fall, we plan to move the STIS data processing to the On-The-Fly-Reprocessing (OTFR) system. Under OTFR, data will be reprocessed from the original "pod" file, which is the earliest telemetry product received for an exposure at STScI. We will present the reasons behind this move, the benefits it will provide, and what changes you can expect to see.