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We present Spitzer observations of the dark globule CB190 (L771). We observea roughly circular 24 micron shadow with a 70 arcsec radius. The extinctionprofile of this shadow matches the profile derived from 2MASS photometry at theouter edges of the globule and reaches a maximum of ~32 visual magnitudes atthe center. The corresponding mass of CB190 is ~10 Msun. Our 12CO and 13CO J =2-1 data over a 10 arcmin X 10 arcmin region centered on the shadow show atemperature ~10 K. The thermal continuum indicates a similar temperature forthe dust. The molecular data also show evidence of freezeout onto dust grains.We estimate a distance to CB190 of 400 pc using the spectroscopic parallax of astar associated with the globule. Bonnor-Ebert fits to the density profile, inconjunction with this distance, yield xi_max = 7.2, indicating that CB190 maybe unstable. The high temperature (56 K) of the best fit Bonnor-Ebert model isin contradiction with the CO and thermal continuum data, leading to theconclusion that the thermal pressure is not enough to prevent free-fallcollapse. We also find that the turbulence in the cloud is inadequate tosupport it. However, the cloud may be supported by the magnetic field, if thisfield is at the average level for dark globules. Since the magnetic field willeventually leak out through ambipolar diffusion, it is likely that CB190 iscollapsing or in a late pre-collapse stage.

Spitzer observations of a 24 micron shadow: Bok Globule CB190