Spitzer observations of a 24 micron shadow: Bok Globule CB190

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.

16 pages, 13 figures, accepted for publication in ApJ

References in corpus (21)

• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Interstellar Dust Grains
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Scattering by Interstellar Dust Grains: Optical and Ultraviolet
• Systematic Molecular Differentiation in Starless Cores
• 2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence
• Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
• Reduction Algorithms for the Multiband Imaging Photometer for Spitzer
• Near Infrared Imaging Survey of Bok Globules: Density Structure
• Dynamic cores in hydrostatic disguise
• Ambipolar-Diffusion Timescale, Star-Formation Timescale, and the Ages of Molecular Clouds: Is There a Discrepancy?
• The NGC 7129 Young Stellar Cluster: A Combined Spitzer, MMT, and 2MASS Census of Disks, Protostars, and Outflows
• Modeling the Physical Structure of the Low Density Pre-protostellar Core Lynds 1498
• From Dusty Filaments to Cores to Stars: An Infrared Extinction Study of Lupus 3
• The initial conditions of isolated star formation - VII. Spitzer mapping of pre-stellar cores
• Envelope Structure of Starless Core L694-2 Derived from a Near-Infrared Extinction Map
• Fragmentation Instability of Molecular Clouds: Numerical Simulations
• Large Scale CO and [CI] emission in the rho Ophiuchi Molecular Cloud
• The kinetic temperature of Barnard 68
• Discovery of a Dusty Ring in the Coalsack: A Dense Core Caught in the Act of Formation?

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