Dense cores in dark clouds. I. CO observations and column densities of high-extinction regions.

Ninety small (approximately 5 arcmin) visually opaque regions selected for Palomar Sky Atlas prints are surveyed in the 2.7 mm J = 1 - 0 lines of C(O-18) and (C-13)O. The regions are for the most part in complexes of obscuration, including those in Taurus and Ophiuchus. The typical C(O-18) emission region has a C(O-18) line width of 0.6 km/s, an optical depth of 0.4, an excitation temperature of 10 K, and a column density of 2 x 10 to the 15th per sq cm. It has a size of 0.3 pc, a visual extinction of approximately 11 mag, and a mass of approximately 30 solar masses. A comparison with equilibrium and collapse models suggests that purely thermal supporting motions are consistent with the present data, although this is considered unlikely. It is pointed out that if the full C(O-18) line width reflects turbulent supporting motions, nearly all of the observed clouds are consistent with stable equilibrium. If only part of the C(O-18) line width reflects supporting motions, a number of clouds are also consistent with turbulent contraction.