Water Masers Embedded in Ultracompact HII Regions in the W75N Cloud Core

Details Water Masers Embedded in Ultracompact HII Regions in the W75N Cloud Core Water Masers Embedded in Ultracompact HII Regions in the W75N Cloud Core

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.3701h&link_type=abstract

American Astronomical Society, 182nd AAS Meeting, #37.01; Bulletin of the American Astronomical Society, Vol. 25, p.853

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present high-resolution radio continuum, H2O 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 H2O maser emission from W75N with the 32-m Medicina telescope. Since H2O 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 H2O 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->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->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.

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