TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. III. G59.7+0.1 AND W 51 IRS2

We report trigonometric parallaxes for G59.7+0.1 and W 51 IRS2, corresponding to distances of 2.16+(0.10)(-0.09) kpc and 5.1+(2.9)(-1.4) kpc, respectively. The distance to G59.7+0.1 is smaller than its near kinematic distance and places it between the Carina-Sagittarius and Perseus spiral arms, probably in the Local (Orion) spur. The distance to W 51 IRS2, while subject to significant uncertainty, is close to its kinematic distance and places it near the tangent point of the Carina-Sagittarius arm. It also agrees well with a recent estimate based on O-type star spectro/photometry. Combining the distances and proper motions with observed radial velocities gives the full space motions of the star-forming regions. We find modest deviations of 5-10 km s(-1) from circular Galactic orbits for these sources, both counter to Galactic rotation and toward the Galactic center.