A study of the Cometary Globules in the GUM Nebula

Abstract

Among the smaller interstellar molecular clouds the Cometary Globules (CGs) stand out due to their peculiar morphology. They are characterized by compact, dusty heads with long faintly luminous tails extending on one side and narrow bright rims on the other side. There exists a significant population of CGs in the Gum Nebula. The Gum Nebula is a large structure approximately 125 parsec in radius delineated by H-alpha emitting filaments. The true nature of the Gum Nebula is ill understood. The CGs in the Gum Nebula are distributed over a region approximately 80 parsec in radius with their tails pointing away from an apparent common center. In the visible region these globules have bright rims on the side facing the common central region. Some of the heads have embedded young stars. In the region bounded by the CGs there are a few massive hot stars including zeta Puppis believed to be the most luminous star in the southern sky. It has been suspected that the morphological appearance of the CGs may be due to the influence of these stars. A detailed study of the system aimed at understanding its origin and kinematics was undertaken using the 10.4m millimeter-wave radio telescope at the Raman Research Institute (Sridharan 1992a,b). The study consisted of (12)CO observations of the heads and the tails of the CGs using the J = 1 to 0 millimeter-wave rotational transition of the carbon monoxide molecule. In addition, the Globule No. 22 was mapped in both (12)CO and (13)CO