Kinematics of OB-associations and the new reduction of the Hipparcos data

Abstract

The proper motions of OB-associations computed using the old and new reductions of the Hipparcos data are in good agreement with each other. The Galactic rotation curve derived from an analysis of the line-of-sight velocities and proper motions of OB-associations is almost flat in the 3-kpc neighbourhood of the Sun. The angular rotation velocity at the solar distance is Ω₀ = 31 +/- 1 km s^-1 kpc^-1. The standard deviation of the velocities of OB-associations from the rotation curve is σ = 7.2 km s^-1. The distance scale for OB-associations should be shortened by 10-20 per cent. The residual velocities of OB-associations calculated for the new and old reductions differ, on average, by 3.5 km s^-1. The mean residual velocities of OB-associations in the stellar-gas complexes depend only slightly on the data reduction employed.