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Millimetre observations of southern translucent clouds
Millimetre emission line observations of ^12^CO J=1-0 are presented fora sample of translucent molecular clouds previously studied by opticalabsorption lines towards background stars. The CO maps provideinformation on the extent, structure, mass and kinematics of theregions. In some clouds, the emission is characterized by a singlecomponent which does not vary much across the region. In other cases,multiple close-lying components or sheets are found, which may vary in aself-similar manner across the cloud. None of the clouds is close tosimple virial equilibrium. Sensitive searches for ^13^CO and C^18^OJ=1-0 emission have been made towards the stellar positions. C^18^O hasbeen detected in only 5 clouds, most of which have extinctions well inexcess of 2 mag. The inferred ^13^CO/C^18^O abundance ratios range from7-25, and the lower limits from >13 to >35. These values are asmuch as five times larger than the overall interstellar([^13^C].[^16^O])/([^12^C] .[^18^O]) ratio, suggesting thatisotope-selective photodissociation plays a role in at least some of theclouds. Searches for other molecules at millimetre wavelengths have beenmade for a few of the best characterized clouds. Surprisingly, noemission was detected from the C_2_H or C_3_H_2_ molecules, even thoughthe abundances of diatomic C_2_ and CH are quite large. On the otherhand, the abundance of HCO^+^ appears comparable to that found in denserclouds, and the abundance of HCN may be up to an order of magnitudelarger than the predictions of models in two clouds.
| A multi-wavelength analysis of interstellar CN - Comparison of red and violet absorption line observations
New measurements of interstellar CN in translucent molecular clouds arepresented. The CN is observed by optical absorption lines in both the B2Sigma(+) violet and A 2Pi - X 2Sigma(+) red systems and through the N =1-0 emission lines at 113.491 GHz. It is shown how the unsaturated linesof the red system can be used to determine the Doppler parameter b andthus to assess the saturation corrections in the analysis of thestronger lines of the violet system. In all cases, the Doppler parameteris small, b less than about 1 km/s, and agrees well with the velocitydispersion obtained from (C-13)O millimeter emission of lines in thesame direction but averaged over a different volume of gas.
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