Trigonometric Parallaxes of Massive Star-Forming Regions. I. S 252 & G232.6+1.0

We are conducting a large program with the NRAO Very Long Baseline Array (VLBA) to measure trigonometric parallaxes of massive star-forming regions across the Milky Way. Here we report measurement of the parallax and proper motion of methanol masers in S 252 and G232.6+1.0. The parallax of S 252 is 0.476 ± 0.006 mas (2.10^+0.027 _-0.026 kpc), placing it in the Perseus spiral arm. The parallax of G232.6+1.0 is 0.596 ± 0.035 mas (1.68^+0.11 _-0.09 kpc), placing it between the Carina-Sagittarius and Perseus arms, possibly in a Local (Orion) spur of the Carina-Sagittarius arm. For both sources, kinematic distances are significantly greater than their parallax distances. Our parallaxes and proper motions yield full space motions accurate to ≈1 km s^-1. Both sources orbit the Galaxy ~13 km s^-1 slower than circular rotation.