HII regions in collapsing massive molecular clouds

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 solar masses/yr results. When 100 O-stars are placed at the center of a freely falling cloud of 300,000 solar masses no evaporation takes place. Rotating clouds collapse to disks and the champagne flow can evaporate the cloud at a higher rate. It is concluded that massive clouds containing OB-stars have lifetimes of no more than 10-million yr.