The IRS peak-up arrays provided science-quality imaging capability in the wavelength range that falls between that covered by IRAC and MIPS, and as such were of interest for imaging alone. For Cycle 2, a new AOT was made available to allow Peak-Up Imaging (PUI) observations. Both a red (18.5-26.0 micron) and a blue (13.3-18.7 micron) filter were available. The red filter provided images over a similar wavelength window as the MIPS 24 micron mode. Information regarding the field-of-view, distortion, and WCS for PUI are provided in Section 2.7.
The peak-up apertures were imaged onto the IRS SL detector array. A read-out of the array therefore also yielded SL1 and SL2 spectra at parallel locations on the sky. The locations of the slits were determined by the orientation of the telescope, which depended on the date of observation. Nonetheless, science quality spectra were obtained. The similarity in PUI and spectroscopic data reduction procedures ensured that the observer received fully calibrated 2D spectra along with the imaging data. Unlike peak-up images taken for the purpose of aligning objects in the slit for spectroscopy, the PUI mode produces science-quality data obtained in the sample-up-the-ramp (SUR) readout, as described in Section 2.9.3.3.
