Improving the Rectification of Spectral Images

Single rows in STIS rectified spectral images are being analyzed in science programs where the highest obtainable spatial resolution is needed. Here we discuss two problems that have limited the accuracy of the rectified spectral images produced by the STScI pipeline: (1) the changing tilts of the spectral traces across the detector have not been taken into account, and (2) interpolation between rows of spectral images which are undersampled in the cross-dispersion direction has produced substantial artifacts in single rows of the rectified images. To address these problems, post-pipeline software is being developed to produce contemporary traces for science exposures, and the time evolution of traces is being characterized so that it can be incorporated into trace reference files. A technique of iteratively subdividing pixels in the cross-dispersion direction, using area interpolation instead of point interpolation, is being developed for a calibration routine which will produce improved rectified images. Preliminary results of the use of these new techniques will be presented here.