ASpitzer Space TelescopeInfrared Spectrograph Spectral Atlas of Luminous 8 μm Sources in the Large Magellanic Cloud

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS)spectra of highly luminous, compact mid-infrared sources in the LargeMagellanic Cloud. Sources were selected on the basis of infrared colors and 8micron (MSX) fluxes indicative of highly evolved, intermediate- to high-massstars with current or recent mass loss at large rates. We determine thechemistry of the circumstellar envelope from the mid-IR continuum and spectralfeatures and classify the spectral types of the stars. In the sample of 60sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch(AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGBstars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We findthat the overwhelming majority of the sample AGB stars (with typical IRluminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects arepredominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine meanbolometric corrections to the stellar K-band flux densities and find that forcarbon stars, the bolometric corrections depend on the infrared color, whereasfor RSGs, the bolometric correction is independent of IR color. Our resultsreveal that objects previously classified as PNe on the basis of IR colors arein fact compact HII regions with very red IRS spectra that include strongatomic recombination lines and PAH emission features. We demonstrate that theIRS spectral classes in our sample separate clearly in infrared color-colordiagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxesderived from the IRS spectra. On this basis, we suggest diagnostics to identifyand classify, with high confidence levels, IR-luminous evolved stars and HIIregions in nearby galaxies using Spitzer and near-infrared photometry.Comment: 46 pages, 9 figures; accepted for publication in AJ; abstract abridge