The evolutionary stage of H II region and spectral types of massive stars from kinematics of H₂0 masers in W51 main

We report relative proper motion measurements of H₂O masers in massive star-forming region W51 Main, based on data sets of VLBI observations for H₂O masers at 22 GHz with Japanese VERA telescopes from 2003 to 2006. Data reductions and single-beam imaging analysis are to measure internal kinematics of maser spots and eventually to estimate the three-dimensional kinematics of H₂O masers in W51 Main. Average space motions and proper motion measurements of H₂O masers are given both graphical and in table formats. We find in this study that W51 Main appears to be associated with hyper-compact H II region with multiple massive proto-stars whose spectral types are of late O.