Ultracompact HII regions in W49N at 500 AU scales: Shells, winds, and the water maser source

We have observed the ionized gas in the star-forming region W49N with the N ational Radio Astronomy Observatory Very Large Array (VLA) at 13 mm and 7 m m, and with the Berkeley Illinois Maryland Association (BIMA) Array at 3.3 mm. These observations vary in resolution from 0." 045 to 0." 35 (500 AU to 4000 AU at a distance of 11.4 kpc). In addition, we have used the VLA to o bserve water maser emission towards the bright W49N:G sources over a wide v elocity range from -435 to 435 km s(-1) The high-resolution continuum obser vations reveal the morphologies in the ultracompact sources; most of the so urces at 0.045 " resolution appear to have shell or ring morphologies. The 3.3 mm emission observed with the BIMA array is dominated by free-free emis sion in ail of the compact sources. There is no evidence for any spectral b reaks corresponding to the emergence of a dust component. Of the seven brig ht sources in W49N for which multifrequency flux densities have been measur ed, four are observed to have rising spectral indices, with values ranging from alpha = 0.3-1.1 and three are observed to be flat (S-nu proportional t o nu(alpha)). Those sources with rising spectral indices (A, B1, B2, G1, an d G2) also have the broadest radio recombination lines, with Delta V-FWHM > 45 km s(-1) in the H66 alpha line (De Free, Mehringer, & Goss). High-resol ution 1.3 cm continuum images made at the same time as the water maser obse rvations have been used to align the maser positions with the high-resoluti on 7 mm continuum to within 0." 05. The maser positions are closely associa ted with the G1/G2 sources. The outflow traced by the water masers (Gwinn, Moran & Reid) appears to be centered within 0.2 " of the G2 peak, the brigh test continuum source in the region, but it remains unclear whether this so urce drives the outflow.