DERIVATION OF THE GALACTIC ROTATION CURVE USING SPACE VELOCITIES

We present rotation curves of the Galaxy based on the space-velocities of 197 OB stars and 144 classical cepheids, respectively, which range over a galactocentric distance interval of about 6 to 12 kpc. No significant differences between these rotation curves and rotation curves based solely on radial velocities assuming circular rotation are found. We derive an angular velocity of the LSR of Omega_0 = 5.5 +/- 0.4 mas/a (OB stars) and Omega_0 = 5.4 +/- 0.5 mas/a (cepheids), which is in agreement with the IAU 1985 value of Omega_0 = 5.5 mas/a. If we correct for probable rotations of the FK5 system, the corresponding angular velocities are Omega_0 = 6.0 mas/a (OB stars) and Omega_0 = 6.2 mas/a (cepheids). These values agree better with the value of Omega_0 = 6.4 mas/a derived from the VLA measurement of the proper motion of SgrA*.