Kinematics of the Galaxy from OB Stars with Data from the Gaia DR2 Catalogue

Abstract

We have selected and analyzed a sample of OB stars with known line-of-sight velocities determined through ground-based observations and with trigonometric parallaxes and propermotions from the Gaia DR2 catalogue. Some of the stars in our sample have distance estimates made from calcium lines. A direct comparison with the trigonometric distance scale has shown that the calcium distance scale should be reduced by 13%. The following parameters of the Galactic rotation curve have been determined from 495 OB stars with relative parallax errors less than 30%: (U, V,W)_⊙ = (8.16, 11.19, 8.55)± (0.48, 0.56, 0.48) km s⁻¹, Ω₀ = 28.92 ± 0.39 km s⁻¹ kpc⁻¹, Ω'₀ = −4.087 ± 0.083 km s⁻¹ kpc⁻², and Ω″ ₀ = 0.703 ± 0.067 km s−1 kpc⁻³, where the circular velocity of the local standard of rest is V0 = 231 ± 5 km s⁻¹ (for the adopted R₀ = 8.0 ± 0.15 kpc). The parameters of the Galactic spiral density wave have been found from the series of radial, V_R, residual tangential, ΔV_circ, and vertical, W, velocities of OB stars by applying a periodogram analysis. The amplitudes of the radial, tangential, and vertical velocity perturbations are f_R = 7.1± 0.3 km s⁻¹, f_θ = 6.5 ± 0.4 km s⁻¹, and f_W = 4.8± 0.8 km s⁻¹, respectively; the perturbation wavelengths are λ_R = 3.3 ± 0.1 kpc, λ_θ = 2.3 ± 0.2 kpc, and λ_W = 2.6 ± 0.5 kpc; and the Sun’s radial phase in the spiral density wave is (χ_⊙)_R = −135◦ ± 5◦, (χ_⊙)θ = −123◦ ± 8◦, and (χ_⊙)_W = −132◦ ± 21◦ for the adopted four-armed spiral pattern.