Trigonometric Parallaxes of Star Forming Regions in the Perseus Spiral   Arm
  We report trigonometric parallaxes and proper motions of water masers for 12 massive star forming regions in the Perseus spiral arm of the Milky Way as part of the Bar and Spiral Structure Legacy (BeSSeL) Survey. Combining our results with 14 parallax measurements in the literature, we estimate a pitch angle of 9.9 +/- 1.5 degrees for a section of the Perseus arm. The three-dimensional Galactic peculiar motions of these sources indicate that on average they are moving toward the Galactic center and slower than the Galactic rotation. 
Y. K. Choi, K. Hachisuka, M. J. Reid, Y. Xu, A. Brunthaler, K. M.   Menten, and T. M. Dame
astro-ph.GA