摘要

Interstellar H2O and OH masers associated with massive star-forming regions can be classified into three morphological types: isolated H2O masers; isolated OH masers; and spatially overlapping OH/H2O maser groups. In a large sample of star-forming regions the total number of maser groups of each type is approximately equal. In order to account for these statistics we propose a pumping scheme based on a broadband radiative pump which produces inverted populations of both OH and H2O masers by a process involving predissociation and dissociation of H2O. This scheme overcomes some drawbacks of earlier radiative pumping models, and may account for the association of OH and H2O masers in massive star forming regions.