H2O masers in W49 North and Sagittarius B2

Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22 GHz H2O maser lines as well as the 22 GHz continuum for the H II regions W49N and Sagittarius B2. The angular resolution of both observations is similar to 0."1, which at the distance of W49N (11.4 kpc) and Sgr B2 (8.5 kpc) corresponds to a physical size of less than 1000 AU in both sources. The velocity coverage for W49N is +/- 435 km s(-1); positions for 316 H2O maser components were obtained. The velocity coverage for Sgr B2 is - 40 to + 120 km s(-1); positions for 68 maser components were determined in Sgr B2 Main, 79 in Sgr B2 North, 14 in Sgr B2 Mid-North, and 17 in Sgr B2 South, for a total of 178 H2O maser positions in Sgr B2. The cross calibration scheme of Reid & Menten was used. Using this procedure, high dynamic range continuum images were obtained with accurate registration (sigma similar to 0."01) of the continuum and maser positions. A detailed comparison between H II components and maser positions for both Sgr B2 and W49N is presented. In Sgr B2 Main, the H2O masers are predominantly located at the outside edge of the high-frequency continuum, lending support to the proposal that entrainment by stellar winds may play an important role in H2O maser emission.