AAS 201st Meeting, January, 2003
Session 112. The ISM: Clouds and Regions
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[112.13] Depletion of CO in MSX Infrared-Dark Clouds

P.A. Feldman, R.O. Redman (HIA/NRCC), S.J. Carey (IPAC/Caltech), F. Wyrowski (MPIfR, Bonn)

We present JCMT, BIMA, and MSX images of three MSX Infrared-Dark Clouds (IRDCs) characterized by cold, dense gas exhibiting high extinction (Av > 100 magnitudes). In the IRDCs observed to date, N2H+(1-0) emission appears to follow the SCUBA 850-micron emission and the MSX 8-micron absorption rather well, but CO appears to be depleted in some regions of high dust column density. G81.50+0.14 P3 and G28.34+0.06 P5 are CO-depleted by factors of > 5 and 2-3, respectively, compared to the other bright, compact sources in their IRDCs. Both sources appear to be unusually cold (7-9K depending on the dust emissivity spectral index in the range 2.5 to 1.5) based on the ratio of the SCUBA flux densities at 450 and 850 microns. Targeted observations by Carey et al. (this meeting) of several locations with particularly high 8-micron extinctions show that many molecular species are depleted in the MSX IRDCs.

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