Galactic kinematics of Cepheids from Hipparcos proper motions

The Hipparcos proper motions of 220 galactic Cepheids, together with relevantground-based photometry, have been analysed. The effects of galactic rotationare very clearly seen. Mean values of the Oort constants, A = 14.82 +/- 0.84km/s/kpc, and B = -12.37 +/- 0.64 km/s/kpc, and of the angular velocity ofcircular rotation at the Sun, Omega_0 = 27.19 +/- 0.87 km/s/kpc, are derived.Comparison of the value of A with values derived from recent radial velocitysolutions confirm, within the errors, the zero-points of the PL and PLCrelations derived directly from the Hipparcos trigonometrical parallaxes of thesame stars. The proper motion results suggest that the galactic rotation curveis declining slowly at the solar distance from the galactic centre (dTheta/dR =-2.4 +/- 1.2 km/s/kpc). The component of the solar motion towards the NorthGalactic Pole is found to be +7.61 +/- 0.64 km/s. Based on the increaseddistance scale deduced in the present paper the distance to the galactic centrederived in a previous radial velocity study is increased to R_0 = 8.5 +/- 0.5kpc.Comment: MNRAS in press, 9 Pages, 6 postscript figures, LaTeX using mn.sty, 8 LaTeX tables separate from main pape