INSTITUTE Instrument Science Report STIS 2009 - 02 STIS CCD Performance after SM 4 : Read Noise , Dark Current , Hot Pixel Annealing , CTE , Gain , and Spectroscopic Sensitivity

We describe the overall performance of the STIS CCD after HST Servicing Mission #4 and the associated updates to calibration reference files. Most aspects of CCD performance are found to be fairly consistent with extrapolations of the trends seen prior to the failure of STIS in August 2004. The CCD gain value for the CCDGAIN = 4 setting has been redetermined using net count ratios of standard star spectra taken in the CCDGAIN = 1 and CCDGAIN = 4 settings, resulting in a gain value of 4.016 ± 0.003 e/DN, which is 0.5% lower than the value used for the calibration of archival STIS CCD data taken before August 2004. Finally, we identify two independent indications of a temperature dependence of the Charge Transfer Efficiency (CTE). However, more calibration data are needed to verify the significance of this effect and, if verified, to calibrate it as a function of CCD housing temperature (as a proxy for CCD chip temperature). This option will be reassessed later during the Cycle 17 calibration program.