Water Masers Embedded in Ultracompact HII Regions in the W75N Cloud Core
Session 37 -- Interferometry
Display presentation, Tuesday, 9:30-6:30, Pauley Room

## [37.01] Water Masers Embedded in Ultracompact HII Regions in the W75N Cloud Core

T.R.Hunter, G.B.Taylor, T.G.Phillips (Caltech), M.Felli, G.Tofani (Arcetri)

We present high-resolution radio continuum, H$_{2}$O maser emission, and molecular line maps of the W75N star-forming region. In addition, we present results from a six-year monitoring campaign of the H$_{2}$O maser emission from W75N with the 32-m Medicina telescope. Since H$_{2}$O masers are usually found to be displaced from compact continuum sources in star-forming regions, it has been conjectured that the masers trace young stellar objects at an earlier stage of evolution, perhaps related to energetic molecular outflows. Using the VLA in A-configuration, we find that the 22 GHz H$_{2}$O maser spots in W75N spatially coincide with weak ultracompact ($<1''$) radio continuum sources located in the dense molecular cloud core. The masers and continuum sources extend a few arc seconds along a roughly N-S line, a feature also evident as an elongation in the peak of the CS J=7$\rightarrow$6 map taken at the CSO. This structure suggests a nearly edge-on, warm, dense disk surrounding the central ionizing source. Past VLBI observations of OH emission have shown a ridge of maser spots along the continuum emission feature, possibly evidence for a shock front in the proposed disk. As a tracer of outflowing molecular gas, we present a map of the CO J=3$\rightarrow$2 line wings at $20''$ resolution, also from the CSO. Due to foreground contamination of the blue wing, only a monopolar red wing is observed on this scale. We believe W75N to be an important source for further study as it may help unify the various evolutionary features of massive star formation.