Spatial Scans with the STIS CCD

Spatial scanning with the STIS CCD is a recently enabled, available-but-unsupported mode for obtaining high S/N ratio spectra of relatively bright targets by trailing the target in the cross-dispersion direction within one of the long STIS apertures. Expected scientific applications include the reliable detection of weak stellar and interstellar absorption features (particularly in the red and near-IR, where ground-based observations can be severely compromised by strong telluric absorption) and accurate time-series monitoring of bright sources (e.g., for characterizing brown dwarfs and transiting exoplanets). Advantages of the spatial scanning mode include: (1) collecting more photons before reaching detector saturation; (2) spreading the photons over a larger area of the detector (enabling better averaging over flat-field variations); (3) improved removal of the IR fringing pattern; and (4) the availability of a wider variety of methods to detect and remove hot pixels and cosmic rays. In this contribution, we discuss possible/recommended uses for this relatively new observing mode and provide information on how to design the observations.