Trigonometric parallaxes of massive star forming regions: G012.88+0.48 and W33

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(-0.15)(+0.17) 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.