17.6 Cycle 9 Calibration

The STIS Cycle 9 calibration plan was modeled closely on the Cycle 8 calibration plan. Supported modes were monitored for items such as sensitivity changes, flat field evolution, and dispersion solutions.

In addition to monitoring instrument health and safety and maintaining the overall calibration of STIS supported modes at the accuracies as established during Cycles 7 and 8, a few special calibration programs were added for Cycle 9, with the following goals:

1. To improve the Charge Transfer Efficiency (CTE) characterization for the CCD, i.e., its dependences on time, source intensity, source nature (point source vs. extended source), and sky background;
2. To quantify the remanence intensity level after over-illumination of the CCD as a function of time after saturation and of number of readouts after saturation. The remanence level may well have increased since STIS was installed on HST due to the degraded CTE;
3. To improve PSF characterization for the CCD in imaging mode, coronagraphic mode, and spectroscopic mode as a function of source color;
4. To improve the dispersion solutions for the reddest settings of the G750M grating;
5. To model the ghosts (which are caused by multiple reflections in the CCD window) in the G750M grating mode.

The results of all the Cycle 9 calibration programs are presented in the close-out report STIS ISR 2003-02.