Local Kinematics of Classical Cepheids

Abstract

Combining Hipparcos proper motions and the radial velocity data, we have studied the Cepheid kinematics on the basis of the three-dimensional Ogorodnikov-Milne model. The results seem to show a slight contracting motion of the Galaxy in the solar neighbourhood, ∂ V_θ / ∂θ / R = ‑2.60 ± 1.07 km s^-1 kpc^-1, which is along the solar circle. Under the hypothesis of a circular stream model, we have determined the galactic rotation V_θ = ‑240.5 ± 10.2 km s^-1 for the classical Cepheids.