R CrB Candidates in the Small Magellanic Cloud: Observations of Cold Featureless Dust with the Spitzer Infrared Spectrograph
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
Pagination or Media Count:
We observed 36 evolved stars in the Small Magellanic Cloud SMC using the low-resolution mode of the Infrared Spectrograph IRS on the Spitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, have nearly featureless spectral energy distributions over the IRS wavelength range 5.2-35 micrometers and Fsub-nu peaking at 8-9 micrometers. The data can be fit by sets of amorphous carbon shells or by single 600-700 K blackbodies. The most similar spectra found in extant spectral databases are of R CrB, although the spectral structure seen in R CrB and similar stars is much weaker or absent in the SMC sources. Both SMC stars show variability in the near-infrared. Ground-based visual spectra confirm that MSX SMC 155 is carbon-rich, as expected for R CrB RCB stars, and coincides with an object previously identified as an RCB candidate. The temperature of the underlying star is lower for MSX SMC 155 than for typical RCB stars. The strength of the Csub-2 Swan bands and the low temperature suggest that it may be a rare DY Per-type star, only the fifth such identified. MSX SMC 014 represents a new RCB candidate in the SMC, bringing the number of RCB candidates in the SMC to six. It is the first RCB candidate discovered with Spitzer and the first identified by its infrared spectral characteristics rather than its visual variability.
- Infrared Detection and Detectors