Galactic Rotation Derived from OB Stars Using Hipparcos Proper Motions and Radial Velocities

Abstract

We have examined the systematic velocity field of the solar neighborhood, based on Hipparcos (HIgh Precision PARallax COllecting Satellite) proper motions and ground-based radial velocities of about 240 O-B5 stars. The distances of these stars were derived from either Hipparcos parallaxes or the SKYMAP compilation of the spectroscopic parallaxes. Using a first-order approximation, we obtained the galactic rotation at the solar vicinity of V_theta =255.52+/- 8.33 km s^-1 assuming the galactocentric distance of the Sun, RO =8.5 kpc. The slope of the galactic-rotation curve is given by (partial V_theta / partial R)_{R_minisolar} =-1.98+/- 0.98 km s^-1 kpc^-1, and the rotation about the axis pointing to the galactic center is -R^-1partial V_z / partial theta = 1.33+/- 0.90 km s^-1 kpc^-1. Our sample shows neither expansion nor contraction with respect to the Local Standard of Rest (LSR).