Probing Dense, Compact Dark Globules

We present Spitzer observations of two globules: CB190 (L771) and B335 (CB199). In the case of CB190 we observe a roughly circular 24 micron shadow with a 70 arcsec radius. The extinction profile of this shadow matches the profile derived from 2MASS photometry at the outer edges of the globule and reaches a maximum of ∼ 32 visual magnitudes at the center. The corresponding mass of CB190 is ∼ 10 msun. Our HHT ¹²CO and ¹³CO J = 2-1 data over a 10 arcmin×10 arcmin region centered on the shadow show a temperature ∼ 10 K. Bonnor-Ebert fits to the density profile, in conjunction with this distance, yield ξ_max = 7.2, indicating that \co\ may be unstable. The high temperature (56 K) of the best fit Bonnor-Ebert model is in contradiction with the CO and thermal continuum data, leading to the conclusion that the thermal pressure is not enough to prevent free-fall collapse. We also find that the turbulence in the cloud is inadequate to support it. However, the cloud may be supported by the magnetic field, if this field is at the average level for dark globules. Since the magnetic field will eventually leak out through ambipolar diffusion, it is likely that \co\ is collapsing or in a late pre-collapse stage. A detailed discussion of our analysis can be found in Stutz et al. (2007). In the case of B335 we observe an 8 micron shadow which we interpret as evidence for a flattened molecular core with a diameter ∼ 8000 AU, a structure predicted by models and distinct from the previously detected protoplanetary disk, with radius ∼ 200 AU (Stutz et al., 2008, in preparation).