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Session 7 - Molecular Clouds.
Display session, Wednesday, January 07
Exhibit Hall,
Fourteen SBGs were observed in the (J=1\rightarrow 0) rotational lines of ^12CO, ^13CO, and C^18O, using the 14 meter radio telescope of the Five College Radio Astronomy Observatory (FCRAO).Maps were made with the fifteen-element QUARRY 3mm\, array receiver and the 1024 channel FAAS autocorrelator spectrometer. A total of 120 to 360 positions per globule, sampled with half-beam spacing, was observed in the ^13CO, line, mostly over 2.5 by 3 arcmin grids, while 30 to 60 full-beam-sampled C^18O\, and ^12CO\, positions per globule were observed. ^13CO\, and C^18O, were observed with a velocity resolution of less than 0.007km s^-1\, channel ^-1; ^12CO\, was observed with 0.013km s^-1\, channel^-1 resolution.
The median SBG in the sample has an apparent volume density profile which falls off as \sim\, r^-2.6, significantly steeper than found in Yun amp; Clemens' 1991 sample (of which the majority contained YSO candidates) whose mean dust density profile fell off as a much shallower \sim\, r^-1.6.
Overall, assuming a distance of 600 pc, the sample of SBGs is characterized as containing cores of size 0.3\pc. SBGs contain about 10 M_ødot\, of gas, have mean H_2 densities of a few \times 10^3 cm ^-3, and kinetic temperatures of \sim\, 10K. Most SBGs are near virial equilibrium. Using energy balance arguments, half of the SBGs may be quasi-statically contracting, and all of these globules still possess envelopes. The strongest association with cloud contraction is the existence of a relatively large envelope. Rotation is in most cases the least significant source of support against gravitational contraction; in the majority of cases kinetic energy owing to turbulent motions is providing the most support against contraction.
