Spitzer observations of a 24 micron shadow: Bok Globule CB190

TL;DR

This study uses Spitzer and molecular data to analyze the Bok Globule CB190, revealing its structure, temperature, and potential instability, suggesting it may be collapsing or on the verge of star formation.

Contribution

First detailed multi-wavelength analysis of CB190 combining infrared shadow, molecular, and dust data to assess its stability and evolutionary stage.

Findings

Maximum extinction of ~32 magnitudes at the center.

CB190's mass is approximately 10 solar masses.

Evidence suggests the globule is likely collapsing or in a late pre-collapse stage.

Abstract

We present Spitzer observations of the dark globule CB190 (L771). 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 12CO and 13CO J = 2-1 data over a 10 arcmin X 10 arcmin region centered on the shadow show a temperature ~10 K. The thermal continuum indicates a similar temperature for the 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 a star associated with the globule. Bonnor-Ebert fits to the density profile, in conjunction with this distance, yield xi_max = 7.2, indicating that CB190 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 CB190 is collapsing or in a late pre-collapse stage.