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

TL;DR

This study analyzes the proper motions of OB-associations using updated Hipparcos data, confirming a nearly flat Galactic rotation curve near the Sun and suggesting a slight revision of the OB associations' distance scale.

Contribution

It provides a new reduction of Hipparcos data for OB-associations and compares it with previous results, refining the Galactic rotation parameters and distance scale.

Findings

Galactic rotation curve is almost flat near the Sun

Angular velocity at solar distance is 31 +/- 1 km/s/kpc

Distance scale for OB associations should be shortened by 10-20%

Abstract

The proper motions of OB-associations computed using the old (Hipparcos 1997} and new (van Leeuwen 2007) reductions of the Hipparcos data are in a good agreement with each other. The Galactic rotation curve derived from an analysis of line-of-sight velocities and proper motions of OB-associations is almost flat in the 3-kpc neighborhood of the Sun. The angular rotation velocity at the solar distance is Omega_0=31 +/-1 km s-1 kpc-1. The standard deviation of the velocities of OB-associations from the rotation curve is sigma=7.2 km s-1. The distance scale for OB associations (Blaha & Humphreys 1989) should be shortened by 10-20%. 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.