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D.W. Koerner (University of Pennsylvania), E.L.N. Jensen (Swarthmore College), K. Cruz, T.B. Guild (University of Pennsylvania), K. Gultekin (U Maryland)
We present sub-arcsecond thermal infrared imaging of HD 98800, a young quadruple system composed of a pair of low-mass spectroscopic binaries separated by 0.8'', each with a K-dwarf primary. Images at wavelengths ranging from 5 to 24.5 microns show unequivocally that the optical secondary, HD 98800B, is the sole source of a comparatively large infrared excess upon which a silicate emission feature is superposed. The excess is detected only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a best-fit black-body temperature of 146 K. With the assumption that the dust is in radiative equilibrium with the central stars, these characteristics require its location to be in a configuration that is circumbinary to the spectroscopic pair. A simple black-body fit underpredicts emission in the region of the broad silicate feature, however, and the feature itself requires a dust component with temperatures higher than 146 K by at least a factor of two. Further, the spectral slope at sub-millimeter wavelengths is flatter than expected for a collision-induced size-distribution of grains, suggesting a range of temperatures present at longer wavelengths. These facts suggest that the circumbinary dust is not confined to a narrow ring but is wide enough to exhibit a range of temperatures.
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