Astrometry of Galactic Star-Forming Region ON2N with VERA: Estimation of the Galactic Constants

TL;DR

This study used VLBI astrometry of H2O masers in ON2N to precisely measure Galactic constants, including the distance to the region and the Sun's Galactocentric distance and rotation velocity, refining our understanding of Galactic dynamics.

Contribution

The paper provides new, precise measurements of the Galactic constants using VLBI astrometry, offering improved estimates of the Sun's distance from the Galactic center and the Galactic rotation velocity.

Findings

Galactocentric distance of the Sun: 7.80+/-0.26 kpc

Galactic rotation velocity at the Sun: 213+/-5 km/s

Angular rotation velocity of the LSR: 27.3+/-0.8 km/s/kpc

Abstract

We have performed the astrometry of H2O masers in the Galactic star-forming region Onsala 2 North (ON2N) with the VLBI Exploration of Radio Astrometry.We obtained the trigonometric parallax of 0.261+/-0.009 mas, corresponding to the heliocentric distance of 3.83+/-0.13 kpc. ON2N is expected to be on the solar circle, because its radial velocity with respect to the Local Standard of Rest (LSR) is nearly zero. Using present parallax and proper motions of the masers, the Galactocentric distance of the Sun and the Galactic rotation velocity at the Sun are found to be R_0 = 7.80+/-0.26 kpc and Theta_0 = 213+/-5 km/s, respectively. The ratio of Galactic constants, namely the angular rotation velocity of the LSR can be determined more precisely, and is found to be Omega_0=Theta_0/R_0 = 27.3+/-0.8 km/s/kpc, which is consistent with the recent estimations but different from 25.9 km/s/kpc derived from the recommended values of Theta_0 and R_0 by the International Astronomical Union (1985).