Trigonometric Parallaxes of Massive Star Forming Regions : I . S 252 & G 232 . 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 −0.026 kpc), placing it in the Perseus spiral arm. The parallax of G232.6+1.0 is 0.596 ± 0.035 mas (1.68 −0.09 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. Both sources orbit the Galaxy ∼ 13 km s slower than circular rotation. Subject headings: techniques: interferometric — astrometry — spiral arm: Perseus, Crux–Scutum — distances — masers — individual (S 252, G232.6+1.0)