Physics
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........27k&link_type=abstract
Ph. D. thesis, Seoul National University, (1997)
Physics
3
Scientific paper
We have studied the internal structures of the 12 dark globules by using the observations in the radio, infrared, and optical wavelengths. For the radio we have utilized the 13.7 m dish of TRAO and 4 m dish of Nagoya University. For the infrared we used the IRAS data basis. In the optical we performed star-count analysis with the POSS data base. Full mapping observations were made in the 13CO(J = 1 --> 0) transition, while in the 12CO(J = 1 --> 0) cross scan observations were only made. From the column density maps, we identified 18 sub-condensations out of the 12 dark globules. Assuming spherical symmetry for each sub-condensation, we derived various physical properties for all the 18 sub-condensations. As regard to the internal density distribution, the dark globules closely resemble the tidally truncated iso-turbulent clouds. As regard to the dynamical nature, most of the globules are under an iso-turbulent condition and are approximately in the hydrostatic equilibrium. Some of the globules seem to undergo a systematic motion of expansion or contraction. The scaling relations between the line width and radius and between the line width and mass were found to hold true for the small dark globules, too. But the exponents are somewhat larger than the ones for the cores of GMC's. The indices of the scaling relations suggest that the globules are in the hydrostatic equilibrium only in an approximate sense. The stability of the dark globules has been analyzed by using the scalar virial theorem. When the globules are approximated by a uniform sphere of equivalent mass, one third of the equivalent spheres are likely to collapse, one sixth of them are expected to expand, and the rest are in an oscillatory equilibrium. The globules in the diffuse phase of the oscillatory equilibrium may not be detected by conventional means, because they are too rarefied to get CO molecules excited or to shield molecules from UV photons, or because they may not withstand the tidal disruption by neighboring clouds. We let the optical extinction and the IR dust optical depth trace out the dust component of the dark globules. To match the resolutions of the IRAS images at 60 and 100 microns, only the 100 micron flux map was de-convoluted by using the maximum correlation algorithm. The code for MCM has been developed specifically for this purpose. The 60 and 100 micron maps were further corrected for the background flux, and we extract from the observed flux the component emanating from the globule only. Using these maps we calculated the dust optical depth at 100 microns. The distribution of the optical extinction was derived from the star count on the POSS plate. The counting was done with a reseau of size 2' × 2'. The distribution of dust constituent within the dark globules correlate well with that of gas in an overall sense. The 100 micron dust optical depth traces the dust column density better than the 100 micron sky flux does. The relations between τd (100microns) and N(13CO), and between N(13CO) and AV are both fitted better by a polynomial of order 2 rather than by a linear function; thereby, ratio of the CO column density to the dust shows a decreasing tendency with increasing τd (100microns). This strongly indicates that the CO molecules condense onto the dust particles in the dense central part of the dark globules. From this study, we found that the dark globule can be characterized as a tidally truncated iso-turbulent cloud in an approximate hydrostatic equilibrium. Some of them are likely to undergo a gravitational collapse.
No associations
LandOfFree
A Multi-Wavelength Study of 12 Dark Globules does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A Multi-Wavelength Study of 12 Dark Globules, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Multi-Wavelength Study of 12 Dark Globules will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1607342