Trigonometric Parallaxes of Massive Star Forming Regions: III. G59.7+0.1 and W 51 IRS2

TL;DR

This study measures precise distances to two massive star-forming regions using trigonometric parallaxes, revealing their locations within the Galaxy and their motions, which show slight deviations from expected circular orbits.

Contribution

It provides new, accurate distance measurements for G59.7+0.1 and W 51 IRS2, improving understanding of their positions and motions in the Galaxy.

Findings

G59.7+0.1 is closer than previous estimates and located in the Local (Orion) spur.

W 51 IRS2's distance aligns with kinematic estimates and is near the tangent point of the Carina-Sagittarius arm.

Both regions exhibit modest deviations from circular Galactic orbits, indicating complex Galactic dynamics.

Abstract

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 to 10 km/s from circular Galactic orbits for these sources, both counter to Galactic rotation and toward the Galactic center.