Water 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 water 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 ~0.1", which at the distance of W49N (11.4 kpc; Gwinn, Moran, & Reid 1992) and Sgr B2 (8.5 kpc) corresponds to a physical size of <1000 AU in both sources. The velocity coverage for W49N is +/- 435 km/s; positions for 316 water maser components were obtained. The velocity coverage for Sgr B2 is -40 to +120 km/s; 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 water maser positions in Sgr B2.   The cross calibration scheme of Reid & Menten (1990, 1997) was used. Using this procedure, high dynamic range continuum images were obtained with accurate registration (rms ~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 water 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 water maser emission. 
E. J. McGrath, W. M. Goss, C. G. De Pree