Astrometry of Galactic Star-Forming Regions ON1 and ON2N with VERA

We conducted the astrometry of H₂O masers in the Galactic star-forming regions ON1 and ON2N with the VLBI Exploration of Radio Astrometry (VERA). The measured distances to ON1 and ON2N are 2.47+/-0.11 kpc and 3.83+/-0.13 kpc, respectively. In the case that ON1 and ON2N are on a perfect circular rotation, we estimate the angular rotation velocity of the Galactic rotation at the Sun (the ratio of the Galactic constants) to be 28 +/- 2 km s^-1 kpc^-1 using the measured distances and three-dimensional velocity components of ON1 and ON2N. This value is larger than the IAU recommended value of 25.9 km s^-1 kpc^-1, but consistent with other results recently obtained with the VLBI technique.