Astrometry of Galactic Star-Forming Region Onsala 1 with VERA: Estimation of Angular Velocity of Galactic Rotation at the Sun

We conducted the astrometry of H₂O masers in the Galactic star-forming region Onsala 1 (ON 1) with the VLBI Exploration of Radio Astrometry (VERA). We measured a trigonometric parallax of 0.404\ ±\0.017 mas, corresponding to a distance of 2.47\ ±\0.11 kpc. ON 1 appears to be located near the tangent point at a Galactic longitude of 69^∘\!\!\!.54. We estimated the angular velocity of the Galactic rotation at the Sun (the ratio of the Galactic rotation velocity at the Sun to the distance from the Sun to the Galactic center) to be Ω₀=Θ₀ / R₀=$ 28.7$\ ±\ $1.3 km s$⁻¹\ $kpc$⁻¹\ $ using the measured distance and proper motion of ON 1. This value is larger than the IAU recommended value of (220 km s$⁻¹/$8.5 kpc) $=$ 25.9 km s$⁻¹\ $ kpc$⁻¹\ $, but consistent with other results recently obtained with the VLBI technique.