Model of the W3(OH) environment based on data for both maser and   'quasi-thermal' methanol lines
  In studies of the environment of massive young stellar objects, recent progress in both observations and theory allows a unified treatment of data for maser and 'quasi-thermal' lines. Interferometric maser images provide information on the distribution and kinematics of masing gas on small spatial scales. Observations of multiple masing transitions provide constraints on the physical parameters.   Interferometric data on 'quasi-thermal' molecular lines permits an investigation of the overall distribution and kinematics of the molecular gas in the vicinity of young stellar objects, including those which are deeply embedded. Using multiple transitions of different molecules, one can obtain good constraints on the physical and chemical parameters.   Combining these data enables the construction of unified models, which take into account spatial scales differing by orders of magnitude.   Here we present such a combined analysis of the environment around the ultracompact HII region in W3(OH). This includes the structure of the methanol masing region, physical structure of the near vicinity of W3(OH), detection of new masers in the large-scale shock front and embedded sources in the vicinity of the TW young stellar object. 
A.M. Sobolev, E.C. Sutton, D.M. Cragg, P.D. Godfrey