Y. W. Wu , M. J. Reid, N. Sakai , T. M. Dame, K. M. Menten, A. Brunthaler, Y. Xu , J. J. Li , B. Ho, B. Zhang 

Abstract: As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high-mass star-forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well-studied regions:kpc  for M17, kpc for W51, and kpc  for GAL 045.5+00.0. Peculiar motions for all but one source are less than 20 km s？1. We fit a log-periodic spiral to the locations and estimate an average pitch angle of . We find that the section of the arm beyond the tangent point in the first quadrant of the Milky Way appears 15 pc below the IAU-defined Galactic plane.