A new CTE Correction Algorithm for Point Source Spectroscopy with the STIS CCD : Correcting for charge trap filling by the ‘ red halo ’ of the CCD Point Spread Function redward of 8000 Å

The CTE-related loss for spectrophotometry of point sources with the STIS CCD is parametrized in terms of dependencies on the signal level of the source spectrum within the extraction box, the background level, and the signal in the point spread function located between the standard extraction box and the read-out amplifier. Primary constraints on the CTE correction algorithm are provided by estimates of CTE losses using CCD spectra of spectrophotometric standard stars. For point-source spectra taken at the standard reference position at the center of the detector, the algorithm corrects CTE losses as large as 30% to within ∼ 1.5% RMS throughout the wavelength range covered by the first-order CCD modes. This uncertainty is similar to the Poisson noise associated with a resolution element of a spectrum with an extracted signal level of about 2500 electrons per pixel. The results described here supersede those reported in an earlier STIS Instrument Science Report (ISR 2003-03).