HII Regions in Collapsing Massive Molecular Clouds

Abstract

Results of two-dimensional numerical calculations of the evolution of HII regions associated with self-gravitating, massive molecular clouds are presented. Depending on the location of the exciting star, a champagne flow can occur concurrently with the central collapse of a nonrotating cloud. Partial evaporation of the cloud at a rate of about 0.005 M⨀/yr results. When 100 0-stars are placed at the center of a freely falling cloud of 3 105 M⨀ no evaporation takes place. Rotating clouds collapse to disks and the champagne flow can evaporate the cloud at a higher rate (0.01 M⨀/yr). We conclude that massive clouds containing OB-stars have lifetimes of no more than 107 yr.