Observations of OH and ammonia in the direction of T Tauri stars

Abstract

Line emission from OH and NH/sub 3/ has been detected in the direction of small groups of T Tauri stars and the space between them. The ratios of the main and satellite line intensities are consistent, within the uncertainties of measurement, with those expected under conditions of local thermodynamic equilibrium. The molecular emission is confined to dark dust clouds in which the T Tauri stars appear to be immersed, and the linear extents of the molecular clouds are on the order of 1 pc. Excitation temperatures approx.4 K and optical depths approx.1 are inferred for both the OH and NH/sub 3/ transitions. Kinetic temperatures of approx.20 K are inferred from the NH/sub 3/ emission lines, and similar kinetic temperatures are inferred from observations of carbon monoxide emission lines in the same directions. Column densities of approx.10/sup 14/--10/sup 15/ cm/sup -2/ are inferred for OH and NH/sub 3/. Considerations of the excitation of the NH/sub 3/ transitions provide a lower limit to the molecular hydrogen density of n/sub H/2> or approx. =4 x 10/sup 3/ cm/sup -3/ and a lower limit to the total cloud mass of M> or approx. =100M/sub sun/. Most of the mass of the molecular clouds hasmore » been left behind after the fragmentation and gravitational collapse which led to the formation of the T Tauri stars. The available data are not inconsistent with the hypothesis that the molecular clouds are now in a state of hydrostatic equilibrium. Attempts to detect the Zeeman splitting of the OH emission lines led to upper limits of approx.0.1 milligauss for the longitudinal magnetic field strength over regions of approx.0.1 pc in size in three clouds. The color excesses of the T Tauri stars, and the similar angular distribution and radial velocities for the molecular clouds and the T Tauri stars, suggest that small groups of T Tauri stars are embedded within and kinematically associated with the molecular clouds.« less