  We present the Spitzer Atlas of Stellar Spectra (SASS), which includes 159
stellar spectra (5 to 32 mic; R~100) taken with the Infrared Spectrograph on
the Spitzer Space Telescope. This Atlas gathers representative spectra of a
broad section of the Hertzsprung-Russell diagram, intended to serve as a
general stellar spectral reference in the mid-infrared. It includes stars from
all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it
includes some objects of intrinsic interest, like blue stragglers and certain
pulsating variables. All the spectra have been uniformly reduced, and all are
available online. For dwarfs and giants, the spectra of early-type objects are
relatively featureless, dominated by Hydrogen lines around A spectral types.
Besides these, the most noticeable photospheric features correspond to water
vapor and silicon monoxide in late-type objects and methane and ammonia
features at the latest spectral types. Most supergiant spectra in the Atlas
present evidence of circumstellar gas. The sample includes five M supergiant
spectra, which show strong dust excesses and in some cases PAH features.
Sequences of WR stars present the well-known pattern of lines of HeI and HeII,
as well as forbidden lines of ionized metals. The characteristic flat-top shape
of the [Ne III] line is evident even at these low spectral resolutions. Several
Luminous Blue Variables and other transition stars are present in the Atlas and
show very diverse spectra, dominated by circumstellar gas and dust features. We
show that the [8]-[24] Spitzer colors (IRAC and MIPS) are poor predictors of
spectral type for most luminosity classes.
