Distance of W3(OH) by VLBI annual parallax measurement
  The most powerful tool for measuring distances within our Galaxy is the annual parallax. We carried out phase-referencing VLBI observations of H$_{2}$O masers in the star forming region W3(OH) with respect to the extragalactic continuum source ICRF 0244+624 to measure their absolute proper motions. The measured annual parallax is 0.484 $\pm$ 0.004 milli-arcseconds which corresponds to a distance of 2.07^{+0.01}_{-0.02}$ kpc from the sun. This distance is consistent with photometric and kinematic distances from previous observations. 
K. Hachisuka (1), A. Brunthaler (2,1), Y. Hagiwara (3), K. M. Menten   (1), H. Imai (4), M. Miyoshi (5), T. Sasao (6) ((1)MP...