The G11.11-0.12 Infrared-Dark Cloud (see March 2000 Newsletter article) has a filamentary appearance, both in absorption against the diffuse 8m Galactic background, and in emission from cold dust at 850m. Detailed comparison of the dust properties at these two wavelengths reveals that standard models for the diffuse interstellar dust in the Galaxy are not consistent with the observations. The ratio of absorption coefficients within the cloud is , which is well below that expected for the diffuse ISM where . This may be due to the formation of ice mantles on the dust and grain coagulation, both of which are expected within dense regions of molecular clouds. The radial structure of the filament is examined, using the 850µm emission as a probe of the underlying column density. The profile is well represented by a marginally resolved central region and a steeply falling envelope, with , where , indicating that G11.11-0.12 is the first observed filament with a profile similar to that of an isothermal cylinder. The observations are fit by a self-consistent isothermal model with gcm and pc in the northern segment and gcm and pc in the southern segment.

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