IRS-TR 12001: Spectral Pointing-Induced Throughput Error and Spectral   Shape in Short-Low Order 1
  We investigate how the shape of a spectrum in the Short-Low module on the IRS varies with its overall throughput, which depends on how well centered a source is in the spectroscopic slit. Using flux ratios to quantify the overall slope or color of the spectrum and plotting them vs. the overall throughput reveals a double-valued function, which arises from asymmetries in the point spread function. We use this plot as a means of determining which individual spectra are valid for calibrating the IRS. 
G.C. Sloan and D. Ludovici
astro-ph.IM astro-ph.GA