1997A&A...323..931W

Molecular line observations are reported of two regions containing small cometary globules at the edge of the Rosette Nebula. Observations of the CO, 3CO and C¹⁸O J=21,-and CO J=43-molecular lines towards Globule 1, the most prominent of the group, show it has a well-developed head-tail structure, with a head diameter ∼0.4pc, and a tail extending ∼1.3pc behind it. The major axis of the system points about 45 degrees away from the direction to the centre of the Rosette Nebula (which contains the [presumed] illuminating stars), and 20 degrees out of the plane of the sky, along a projected line towards the luminous (924L_☉) infrared source IRAS 06314+0427. The CO lines have a complex velocity structure; with a pronounced broadening at the front of the head (as viewed from IRAS 06314+0427); a velocity gradient ∼1.4km/s along the tail, and material at the front of the head is blue-shifted by ∼0.5km/s compared to surrounding gas. The CO J=21-line intensity peaks towards the front of the head, and along the edges of the tail. The 3CO J=21-antenna temperatures in the head are very similar to those of CO, suggesting very high opacities or column densities, or that there is significant CO self-absorption. There is a narrow rim of CO J=43-emission around the front of the head over a limited velocity range, which correlates with the position of a faint optical rim, and a narrow ridge of 2µm H₂ emission. These data give strong support to the Radiation Driven Implosion (RDI) model of Lefloch and Lazareff (1994 – hereafter LL94), which was developed to explain the physical structure of cometary globules. Using an RDI simulation, a remarkably good fit to the data has been obtained, allowing the CO, 3CO and C¹⁸O spatial structures and velocity field to be modelled. This simulation suggests that Globule 1 is ∼400,000years old, and has a mass ∼50M_☉. Additional observations towards the region close to IRAS 06314+0427 show that it is associated with an intense molecular concentration lying at the northern end of a ∼5pc long molecular ridge, with a mass ∼330M_☉, and lies close to the centre of a shell-like condensation.