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, VR, residual tangential, ΔVcirc, and vertical, W, velocities of OB stars by applying a periodogram analysis. The amplitudes of the radial, tangential, and vertical velocity perturbations are fR = 7.1± 0.3 km s−1, fθ = 6.5 ± 0.4 km s−1, and fW = 4.8± 0.8 km s−1, respectively; the perturbation wavelengths are λR = 3.3 ± 0.1 kpc, λθ = 2.3 ± 0.2 kpc, and λW = 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.