On the Accuracy of Three-dimensional Kinematic Distances

Over the past decade, BeSSeL Survey and VERA project have measured trigonometric parallaxes to approximately 250 massive, young stars using VLBI techniques. These sources trace spiral arms over nearly half of Milky Way. What is now needed are accurate distances such which well Galactic center. Here we analyze potential for addressing this need by combining line-of-sight velocities proper motions yield 3D kinematic distance estimates. For within about 10 kpc Sun, significant systematic uncertainties can occur, generally superior. However, center, robust more than usually be achieved trigonometic parallaxes.