Variations in Frequency and Intensity of 1.35-CENTIMETER H_{2}O Emission Profiles in Galactic H II Regions

Abstract

We report observations of 1.35-cm 6is "523 H2O emission in the galactic sources W3, Ori A, and W49 over the period 1969 January to 1970 June. Remarkable changes have occurred in the complex frequency structure of the line profiles and in the intensity, width, apparent radial velocity, and polarization of the individual features. Each of the features contributing to an HiO profile arises from a separate dense region able to sustain maser emission and associated with an H ii region. The changes in intensity and width of features are consistent with a partially saturated maser in a medium undergoing changes in pump power and gain of the maser. Hyperfine structure and blending of independently varying features can account for the apparent shifts in velocity. On one possible model a typical maser has a gain 10 ", kinetic temperature 500" K, dimensions 1 X 1 X 100 a.u., and H2O density 5 X 10 . The degree of saturation and physical conditions vary greatly, however, from feature to feature.