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 approximate to 1 km s(-1). Both sources orbit the Galaxy similar to 13 km s(-1) slower than circular rotation.