6.1 Introduction to the IRS

The IRS provides the Spitzer Space Telescope with spectroscopic capabilities at two different resolutions spanning the wavelength range from $5.2$ to $38 \; \mu {\rm m}$. The IRS is composed of four separate spectroscopic modules, with two of the modules providing ``low'' spectral resolution of ${\rm R} \sim 64-128$ over ``short'' and ``long'' wavelength ranges of $5.2-14.5 \; \mu {\rm m}$ and $14.0-38 \; \mu {\rm m}$, respectively. The other two modules provide ``high'' spectral resolution of ${\rm R} \sim 600$ over ``short'' and ``long'' wavelength ranges of $9.9-19.6 \; \mu {\rm m}$ and $18.7-37.2 \; \mu {\rm m}$, respectively. Each module has its own entrance slit in the Spitzer focal plane. The low-resolution modules employ long slit designs that allow both spectral and one-dimensional spatial information to be acquired simultaneously on the same detector array. The high-resolution modules use a cross-dispersed echelle design that yields both spectra and limited spatial measurements on the same detector array. A small imaging array (the peak-up array) in the Short-Low (SL) module is used to place objects accurately into any of the IRS entrance slits. A more detailed description of the IRS is available in the SOM. An example of how to use the peak-up array may be found in Chapter 8 of this document.