AAS 207th Meeting, 8-12 January 2006
Session 132 Views of the Magellanic Clouds Across Wavelengths
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[132.08] Spitzer Spectra of 2MASS/MSX Selected Sources in the Small Magellanic Cloud

M.P. Egan (AFRL), S.D. van Dyk (Spitzer Science Center), G.C. Sloan (Cornell University), K.E. Kraemer, S.D. Price (AFRL)

We present results from our Spitzer Space Telescope study of late type stars in the Small Magellanic Cloud (SMC). The source selection and tentative identification of spectral type had been made using color-color data derived fromTwo-micron All-Sky Survey (2MASS) and Midcourse Space Experiment (MSX) measurements and the source identification model previously developed by Egan, van Dyk, and Price (2001) for the Large Magellanic Cloud (LMC). Results of the Spitzer SMC spectral survey show surprises in that many stars expected to be oxygen-rich, high-luminosity asymptotic giants turned out to have carbon-rich envelopes. Overpopulations in the Magellanic Cloud carbon star population, relative to Milky Way samples, have been noted by other research teams. Similar results for a 2MASS/MSX selected sample in the LMC have been found by the Spitzer team led by J. Kastner (Buchanan et al., in press). These results imply that the lower metallicity in the SMC (and LMC) allows much easier evolution to carbon-rich envelope chemistries across all mass ranges for AGB stars than is seen in the Milky Way. This fact has implications for the future use of color-color diagrams for classifying stars in other galaxies. In order to distinguish between C-rich and O-rich AGB stars by color, correct spectral bands must be chosen, and the metallicity and color relationship well understood. We will present the spectra from the Spitzer SMC sample in this paper, and compare 2MASS/MSX colors for the SMC with similar Milky Way samples. We will also examine the theoretical implications of the dearth of OH/IR stars found in the SMC versus previous expectations.

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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.