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We have observed a sample of 35 long-period variables and four Cepheidvariables in the vicinity of 23 Galactic globular clusters using the InfraredSpectrograph on the Spitzer Space Telescope. The long-period variables in thesample cover a range of metallicities from near solar to about 1/40th solar.The dust mass-loss rate from the stars increases with pulsation period andbolometric luminosity. Higher mass-loss rates are associated with greatercontributions from silicate grains. The dust mass-loss rate also depends onmetallicity. The dependence is most clear when segregating the sample by dustcomposition, less clear when segregating by bolometric magnitude, and absentwhen segregating by period. The spectra are rich in solid-state and molecularfeatures. Emission from alumina dust is apparent across the range ofmetallicities. Spectra with a 13-um dust emission feature, as well as anassociated feature at 20 um, also appear at most metallicities. Molecularfeatures in the spectra include H_2O bands at 6.4-6.8 um, seen in both emissionand absorption, SO_2 absorption at 7.3-7.5 um, and narrow emission bands fromCO_2 from 13.5 to 16.8 um. The star Lynga 7 V1 has an infrared spectrumrevealing it to be a carbon star, adding to the small number of carbon starsassociated with Galactic globular clusters.

Spitzer Spectroscopy of Mass Loss and Dust Production by Evolved Stars in Globular Clusters