  We observed a sample of evolved stars in the Large and Small Magellanic
Clouds (LMC and SMC) with the Infrared Spectrograph on the Spitzer Space
Telescope. Comparing samples from the SMC, LMC, and the Galaxy reveals that the
dust-production rate depends on metallicity for oxygen-rich stars, but carbon
stars with similar pulsation properties produce similar quantities of dust,
regardless of their initial metallicity. Other properties of the oxygen-rich
stars also depend on metallicity. As the metallicity decreases, the fraction of
naked (i.e. dust-free) stars increases, and among the naked stars, the strength
of the 8 um absorption band from SiO decreases. Our sample includes several
massive stars in the LMC with long pulsation periods which produce significant
amounts of dust, probably because they are young and relatively metal rich.
Little alumina dust is seen in circumstellar shells in the SMC and LMC, unlike
in Galactic samples. Three oxygen-rich sources also show emission from
magnesium-rich crystalline silicates. Many also show an emission feature at 14
um. The one S star in our sample shows a newly detected emission feature
centered at 13.5 um. At lower metallicity, carbon stars with similar amounts of
amorphous carbon in their shells have stronger absorption from molecular
acetylene (C_2H_2) and weaker emission from SiC and MgS dust, as discovered in
previous studies.
