Galactic kinematics from data on open star clusters from the MWSC catalogue

Abstract

Open star clusters from the MWSC (Milky Way Star Clusters) catalogue have been used to determine the Galactic rotation parameters. The circular rotation velocity of the solar neighborhood around the Galactic center has been found from data on more than 2000 clusters of various ages to be V₀ = 236 ± 6 km s⁻¹ for the adopted Galactocentric distance of the Sun R₀ = 8.3 ± 0.2 kpc. The derived angular velocity parameters are Ω₀ = 28.48 ± 0.36 km s⁻¹ kpc⁻¹, Ω’₀ = −3.50 ± 0.08 km s⁻¹ kpc₋₂, and Ω″₀ = 0.331 ± 0.037 km s⁻¹ kpc⁻³. The influence of the spiral density wave has been detected only in the sample of clusters younger than 50 Myr. For these clusters the amplitudes of the tangential and radial velocity perturbations are f^θ = 5.6 ± 1.6 km s⁻¹ and f_R = 7.7 ± 1.4 km s⁻¹, respectively; the perturbation wavelengths are λ_θ = 2.6 ± 0.5 kpc (i_θ = ⁻¹1◦ ± 2◦) and λ_R = 2.1 ± 0.5 kpc (i_R = −9◦ ± 2◦) for the adopted four-armed model (m = 4). The Sun’s phase in the spiral density wave is (χ_⊙)_θ = −62◦ ± 9◦ and (χ_⊙)_R = −85◦ ± 10◦ from the residual tangential and radial velocities, respectively.