Galactic kinematics derived from classical Cepheids.

Abstract

On the basis of radial velocity and Hipparcos proper motion data, the author has analyzed the galactic kinematics of classical Cepheids. Using the 3-D Ogorodnikov-Milne model he has determined the rotational velocity of the Galaxy to be V₀ = 240.5±10.2 km/s, on assuming a galactocentric distance of the Sun of R₀ = 8.5 kpc. The results clearly indicate a contracting motion in the solar neighbourhood of (θV_θ/θθ)/R = -2.60±1.07 km s^-1kpc^-1, along the direction of galactic rotation. Possible reason for this motion is discussed. The solar motion found here is S_sun = 18.78±0.86 km/s in the direction l_sun = 54.4°±2.9° and b_sun = +26.6°±2.6°.