Proper motions of open star clusters and the rotation rate of the galaxy

The mean proper motions of 167 Galactic open clusters with radial-velocity measurements are computed from the data of the Tycho-2 catalog using kinematic and photometric cluster membership criteria. The resulting catalog is compared to the results of other studies. The new proper motions are used to infer the Galactic rotation rate at the solar circle, which is found to be omega(0) = +24.6 +/- 0.8 km s(-1) kpc(-1). Analysis of the dependence of the dispersion of omega(0) estimates on heliocentric velocity showed that even the proper motions of clusters with distances r > 3 kpc contain enough useful information to be used in kinematic studies demonstrating that the determination of proper motions is quite justified even for very distant clusters. (C) 2003 MAIK Nauka/Interperiodica.