Analysis of galactic rotation from masers based on a nonlinear oort model

Abstract

Based on data on Galactic masers with measured trigonometric parallaxes, we have tested a nonlinear model of Galactic rotation using generalized Oort formulas. This model is shown to yield pretty good results up to heliocentric distances of 3-4 kpc. The main feature of the method is the possibility of estimating the solar Galactocentric distance R 0 . This distance has been found by analyzing ≈60 masers to be R 0 = 8.3 ± 0.4 kpc. Our study of the threedimensional kinematics of more than 100 masers based on the Ogorodnikov-Milne model has shown that significant nonlinearities are present only in the xy plane (rotation around the Galactic z axis) due to the peculiarities of the Galactic rotation curve. No significant linear dependences have been found in the xz and yz planes. We show the presence of a wave in the velocities w as a function of coordinate x or distance R with a wavelength of 3 kpc and an amplitude of 10 km s −1 . The wave is particularly prominent in the Local and Perseus arms.