Kinematics of the galaxy from OB stars with proper motions from the Gaia DR1 catalogue

Abstract

We consider two samples of OB stars with different distance scales that we have studied previously. The first and second samples consist of massive spectroscopic binaries with photometric distances and distances determined from interstellar calcium lines, respectively. The OB stars are located at heliocentric distances up to 7 kpc. We have identified them with the Gaia DR1 catalogue. Using the proper motions taken from the Gaia DR1 catalogue is shown to reduce the random errors in the Galactic rotation parameters compared to the previously known results. By analyzing the proper motions and parallaxes of 208 OB stars from the Gaia DR1 catalogue with a relative parallax error of less than 200%, we have found the following kinematic parameters: (U, V)_⊙ = (8.67, 6.63)± (0.88, 0.98) km s⁻¹, Ω₀ = 27.35 ± 0.77 km s⁻¹ kpc⁻¹, Ω′₀ = −4.13 ± 0.13 km s⁻¹ kpc⁻², and Ω″₀ = 0.672 ± 0.070 km s⁻¹ kpc⁻³, the Oort constants are A = −16.53 ± 0.52 km s⁻¹ kpc⁻¹ and B = 10.82 ± 0.93 km s⁻¹ kpc⁻¹, and the linear circular rotation velocity of the local standard of rest around the Galactic rotation axis is V₀ = 219 ± 8 km s⁻¹ for the adopted R₀ = 8.0 ± 0.2 kpc. Based on the same stars, we have derived the rotation parameters only from their line-of-sight velocities. By comparing the estimated values of Ω′₀, we have found the distance scale factor for the Gaia DR1 catalogue to be close to unity: 0.96. Based on 238 OB stars of the combined sample with photometric distances for the stars of the first sample and distances in the calcium distance scale for the stars of the second sample, line-of-sight velocities, and proper motions from the Gaia DR1 catalogue, we have found the following kinematic parameters: (U, V, W)_⊙ = (8.19, 9.28, 8.79)± (0.74, 0.92, 0.74) km s⁻¹, Ω₀ = 31.53 ± 0.54 km s⁻¹ kpc⁻¹, Ω′₀ = −4.44 ± 0.12 km s⁻¹ kpc⁻², and Ω″₀ = 0.706 ± 0.100 km s⁻¹ kpc⁻³; here, A = −17.77 ± 0.46 km s⁻¹ kpc⁻¹, B = 13.76 ± 0.71 km s⁻¹ kpc⁻¹, and V₀ = 252 ± 8 km s⁻¹.