Abstract

We have investigated the structure of the high galactic-latitude cometary globule 12 (CG 12) by means of radio molecular-line observations. Detailed, high signal-to-noise ratio maps in (CO)-O-18 (1-0), (CO)-O-18 (2-1) and molecules tracing high-density gas, CS (3-2), DCO+ (2-1), and (HCO+)-C-13 (1-0), are presented. The (CO)-O-18 line emission is distributed in a 10' long North-South elongated lane with two strong maxima, CG 12-N(orth) and CG 12-S(outh). In CG 12-S the high-density tracers delineate a compact core, DCO+ core, which is offset by 15" from the (CO)-O-18 maximum. The observed strong (CO)-O-18 emission traces either the surface of the DCO+ core or a separate, adjacent cloud component. The driving source of the collimated molecular outflow detected in 1993 is located in the DCO+ core. The (CO)-O-18 lines in CG 12-S have low-intensity wings possibly caused by the outflow. The emission in high-density tracers is weak in CG 12-N and especially the (HCO+)-C-13, DCO+, and N2H+ lines are +0.5 km s(-1) offset in velocity with respect to the (CO)-O-18 lines. Evidence is presented that the molecular gas is highly depleted. The observed strong (CO)-O-18 emission towards CG 12-N originates in the envelope of this depleted cloud component or in a separate entity seen in the same line of sight. The (CO)-O-18 lines in CG 12 were analysed using positive matrix factorization, PMF. The shape and the spatial distribution of the individual PMF factors fitted separately to the (CO)-O-18 (1-0) and (2-1) transitions were consistent with each other. The results indicate a complex velocity and line excitation structure in the cloud. Besides separate cloud velocity components the (CO)-O-18 line shapes and intensities are influenced by excitation temperature variations caused by e. g., the molecular outflow or by molecular depletion. Assuming a distance of 630 pc the size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the (CO)-O-18 mass larger than 100 M-circle dot are comparable to those of other nearby low/intermediate mass star formation regions.