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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[132.07] Observations of Cold, Carbon-Rich Dust around Evolved Stars in the Small Magellanic Cloud with the {\em Spitzer} Infrared Spectrograph

K. E. Kraemer (AFRL), G. C. Sloan (Cornell Univ.), P. R. Wood (Aus. Nat. Univ.), M. P. Egan, S. D. Price (AFRL)

Three of the 36 evolved stars in the Small Magellanic Cloud (SMC) that we have observed with the Infrared Spectrograph (IRS) on the {\em Spitzer Space Telescope} show unusual mid-infrared spectra dominated by cool dust emission. Two of the stars have nearly featureless spectra over the IRS wavelength range (5.2--35 \micron) which peak at ~8--9 \micron\ (in F\nu units). These spectra can be fit by sets of amorphous carbon shells or by single 600--700 K blackbodies. They are similar to mid-infrared spectra of R CrB (RCB) and related objects observed with the Short Wavelength Spectrometer (SWS) on the {\em Infrared Space Observatory}, although the objects observed with the SWS typically show more spectral features than observed in the SMC sources. The near-infrared and optical properties of the two SMC sources producing these near-featureless spectra are also consistent with RCB candidates. One of the SMC objects has independently been identified as such. The strength of its C2 Swan bands and its low estimated temperature suggest that it may be a rare DY Per-type star, only the fifth such identified. The other RCB candidate is new, raising the number in the SMC to six. This detection is the first based on the infrared properties of such a source and the first discovered with {\em Spitzer}. The third object with a cool dust spectrum in our SMC sample has a spectrum that peaks ~15--17 \micron\ and shows emission features from polycyclic aromatic hydrocarbons (PAHs). This source may already have evolved off of the asymptotic giant branch.

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Bulletin of the American Astronomical Society, 37 #4
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