Trigonometric Parallaxes of Massive Star Forming Regions: G012.88+0.48 and W33

TL;DR

This study uses VLBA measurements to determine precise distances to star-forming regions G012.88+0.48 and W33, revealing their true location in the galaxy and correcting previous overestimations of their luminosity and mass.

Contribution

It provides accurate parallax distances for these regions, clarifying their placement in the spiral arm and revising their physical properties.

Findings

W33 is at about 2.4 kpc, not 3.7 kpc.

W33 is a single complex, not multiple regions.

Luminosity and mass estimates are overestimated by over two times.

Abstract

We report trigonometric parallaxes for water masers in the G012.88+0.48 region and in the massive star forming complex W33 (containing G012.68--0.18, G012.81--0.19, G012.90--0.24, G012.90--0.26), from the Bar and Spiral Structure Legacy (BeSSeL) survey using the Very Long Baseline Array. The parallax distances to all these masers are consistent with $2.40^{+0.17}_{-0.15}$ kpc, which locates the W33 complex and G012.88+0.48 in the Scutum spiral arm. Our results show that W33 is a single star forming complex at about two-thirds the kinematic distance of 3.7 kpc. The luminosity and mass of this region, based on the kinematic distance, have therefore been overestimated by more than a factor of two. The spectral types in the star cluster in W33\,Main have to be changed by 1.5 points to later types.