IRS Peakup Tracking
Many Staring and Spectral Mapping IRS programs include peak-up target acquisition. Since the IRS slits were relatively narrow compared to the nominal pointing accuracy of the Observatory, it was often necessary to perform a peak-up before starting a spectroscopic integration in order to achieve a given photometric accuracy (or even ensure that the target was in the slit). Also, peak-up acquisition allowed observers to obtain a spectrum of a source even if its coordinates were not precisely known -- as long as the target is bright enough for the peak-up to function properly. See the IRS Instrument Handbook for additional information on the Peak-Up Acquisition algorithm.
In the following links, this page tracks Peak-Up Failures (when the peak-up target could not be found) and False Positives (when the peak-up algorithm identified a peak-up target, but it is likely not the intended target).