The IC133 Water Vapor Maser in the Galaxy M33: A Geometric Distance
  We report on the results of a 14 year long VLBI study of proper motions in the IC133 H2O maser source in the galaxy M33. The method of Ordered Motion Parallax was used to model the 3-dimensional structure and dynamics of IC133 and obtain a distance estimate, 800 +/- 180 kpc. Our technique for determining the distance to M33 is independent of calibrations common to other distance indicators, such as Cepheid Period-Luminosity relations, and therefore provides an important check for previous distance determinations. 
A. L. Argon (1), L. J. Greenhill (1), J. M. Moran (1), M. J. Reid (1),   K. M. Menten (2), M. Inoue (3) ((1) Harvard-Smithso...