The IRAS Vela shell: a "super shell" in the making?

Abstract

The IRAS Vela shell was first seen as a ring of infrared emission in the IRAS maps of the Gum-Vela region coincident with the Gum Nebula. We have studied the kinematics of the molecular material (12CO) associated with the IRAS point sources and Southern Dark Clouds seen in this region and established the presence of a giant expanding Shell of molecular gas. The estimated mass, size and expansion velocity of the Shell lead us to conclude that it is the remnant of a GMC, in the process of disintegration through the influence of a central OB association (Vela OB2). This scenario is further strengthened by various other phenomena seen in the region like enhanced star formation, globules with bright rims, clumpy nature of the molecular gas etc., all of which indicate the disruption of a molecular cloud. We conjecture that the IRAS Vela Shell is a nearby example of a ``super shell'' in its early stages of evolution and as such is an ideal opportunity to study these objects now widely seen both in our Galaxy and in new observations of the Magellanic Clouds. We present our observations and conclusions and also comment on the possible evolution of the Shell into a system of star forming complexes like the Gould's belt.