The structure of the cometary globule CG 12: a high-latitude star-forming region ^*,**

¹ Observatory, PO Box 14, University of Helsinki, Finland e-mail: haikala@astro.helsinki.fi
² Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001, Santiago, Chile
³ Onsala Space Observatory, 439 00 Onsala, Sweden e-mail: michael.olberg@chalmers.se

Received: 23 March 2006
Accepted: 22 September 2006

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 C¹⁸O (1-0), C¹⁸O (2-1) and molecules tracing high-density gas, CS (3-2),  (2-1), and (1-0), are presented. The C¹⁸O line emission is distributed in a 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,  core, which is offset by 15´´ from the maximum. The observed strong emission traces either the surface of the  core or a separate, adjacent cloud component. The driving source of the collimated molecular outflow detected in 1993 is located in the  core. The 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 , , and lines are +0.5    offset in velocity with respect to the lines. Evidence is presented that the molecular gas is highly depleted. The observed strong 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 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 (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 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 mass larger than 100  are comparable to those of other nearby low/intermediate mass star formation regions.