Small dense molecular clouds which envelope groups of T-Tauri stars

Dense molecular clouds within the Taurus and NGC 2264 regions have undergone gravitational collapse and fragmentation to form groups of low mass (approximately 1 solar mass) T-Tauri stars which are still embedded within the clouds and which are kinematically associated with them. Molecular column densities on the order of 1014 cm-2 are inferred from the emission lines of OH and NH3. Emission line widths are approximately less than 2 kms-1 and the antenna beamwidths include linear extents of order 0.1 pc. The OH emission appears to be in a condition of local thermodynamic equilibrium, and it cannot arise from circumstellar shells similar to those surrounding the masing infrared stars. The OH and NH3 emission occurs in clouds of approximately 1 pc in extent with optical depths of 0.1 to 1.0 and excitation temperatures of the order of 10K. The molecular clouds have radii of approximately 0.5 pc, molecular hydrogen densities of approximately 4000 cm-3, masses of approximately 100 solar masses, and kinetic temperatures of approximately 20 K. The observed data are not inconsistent with the molecular clouds being in a state of hydrostatic equilibrium. (Auth.)